DVD primer - Educypedia
primer
A DVD Primer
From DV to DVD: Enriching the
Experience of High-Quality Video
TABLE OF CONTENTS
1 Introduction
1
What is DVD?
2
What are the advantages of DVD?
2
The components of DVD technology
5
DVD-Video
6
Video compression
9
Audio for DVD-Video
11 Aspect ratios
17 Multiple camera angles
18 Subpicture streams and closed captions
19 DVD-Video interactivity
20 Menus and navigation
24 Region Coding
25 Content Protection
27 How do I make DVDs?
27 What tools do I need?
31 The DVD workflow
34 Resources
35 Glossary
Introduction
From Stone Age to Bronze Age to Industrial Age to Information Age, humans have found
new ways to communicate and to tell stories that educate, inform, and entertain. Digital
technology has transformed the ways we access and use information more profoundly
than any other human invention, and brought us to the dawn of the Interactive Age.
Within three years of its introduction in September 1997, DVD technology products
outpaced the consumer adoption rate of any other product in history. The online
resource Research and Markets predicts that worldwide DVD recorder shipments will
grow from 9.4 million in 2004 to 67.7 million in 2009. This number does not even count
players, set-top boxes, and computer DVD drives.
While DVD players have rapidly become a standard component of home entertainment
systems, and DVD drives continue to replace CD drives in personal computers, there
are also developments that are changing the way we experience and use video:
•Digital video software and hardware is readily available and affordable, so more
people are producing their own videos—for work or their own entertainment.
•Nonlinear editing software has made capturing video and crafting compelling video
productions affordable and easy.
•DVD allows for richer content than other media. Compact Disc (CD) technology
empowered computer users of all levels to become adept at selecting, organizing, and
storing their own collections of imagery and audio. Today, DVDs bring broadcast
quality video to those users.
This primer introduces you to key concepts of DVD technology and shows you how
easy it can be to develop and author your own DVDs. You’ll learn how you can use
DVD technology to make your video content more dynamic. If you’re a beginner, you’ll
learn enough to be an informed member of a workgroup planning or producing DVD
projects. If you are already creating video productions, this primer will introduce you
to state-of-the-art technology you can use to repurpose your content for DVD distribution.
As you read this primer, you might encounter unfamiliar words or abbreviations. Terms
in boldface are defined in the Glossary and many will also be covered in greater detail
as you read on.
What is DVD?
DVD is an optical disc storage medium similar to CD, but capable of holding far more
data. DVD stands for more than just the disc itself; it represents a whole system of
standards for DVD technology—discs, drives, and players and the formats that support
them. DVD technology offers the higher quality and speed needed to deliver cinemalike video and better-than-CD audio. DVD was originally an abbreviation for Digital
Video Disc. To highlight the flexibility of the format, some industry leaders have suggested that DVD is an abbreviation for Digital Versatile Disc.
What are the advantages of DVD?
DVD has a number of advantages as both a delivery medium for digital media and a portable
storage medium:
• Storage capacity: A CD stores a maximum of 650MB of data. That’s enough for approximately
74 minutes of audio. A DVD stores up to 4.7GB per layer, per side. Using MPEG-2 compression, a single-sided, single-layer DVD can easily accommodate an entire feature-length film
with multichannel digital audio. A DVD-18 disc (currently the highest-capacity format), with
two layers on each side and a capacity just over 17GB, can hold up to eight hours of broadcastquality video.
• Quality: DVD provides almost twice the video resolution of standard VHS videotape. Because
video on DVD is stored digitally, the medium itself does not create noise. As a result, DVD
provides a much clearer picture than analog videotape.
• Convenience and compatibility: Unlike the larger laser disc, a DVD is the same size and thickness as a CD. Computer DVD drives support both CDs and DVDs. DVDs offer interactive
menus that let users randomly navigate content. The interactive capabilities of DVDs provides
unlimited possibilities for creating user experiences.
• Durability: While videotapes eventually wear out or break, DVDs do not suffer loss of fidelity
over time, because they don’t come into direct contact with the player’s mechanics.
Because of its many attributes, DVD meets the demands of a number of industries:
• Computer industry: Recordable and rewritable DVDs provide the next generation of convenience and higher capacity for data storage and archiving. Increasingly complex multimedia
applications are continually being developed and these can easily be delivered on DVD.
• Motion picture industry: The movie industry has embraced DVDs because they can hold a fulllength feature film, while delivering excellent quality video with surround-sound audio.
• Music industry: The high storage capacity enables the music industry to offer products on DVDAudio discs, which deliver higher quality sound than can be achieved on CDs.
• Video game industry: DVD technology delivers realistic video content with longer playing time.
Standards are set by a single association
DVD owes its phenomenal success largely to the organization that governs its standards and
promotes its acceptance—the DVD Forum (www.dvdforum.org). An often uneasy alliance of
hardware manufacturers, software firms, and other users of DVD technology, this international
association was established in 1995 initially as the DVD Consortium by 10 companies: Hitachi,
Matsushita, Mitsubishi, Philips, Pioneer, Sony, Thomson Multimedia, Time-Warner, Toshiba,
and JVC (Victor Company of Japan). Today, virtually every major company involved in DVD
technology is a member of the DVD Forum.
The components of DVD technology
DVD discs look much like CDs. They are the same diameter (120mm) and thickness (1.2mm).
However, each layer (up to two) on each of the two sides of a DVD can hold up to seven times the
data that can be stored on a single-sided, single-layer CD. While the layers on a dual-layer side of
a DVD don’t hold as much data as a single layer side, a double-sided, dual-layer DVD (DVD-18)
can hold up to 17GB of data.
Etched into the surface of the metallic discs that are bonded within the acrylic coatings of both
CDs and DVDs are microscopic marks called pits. The surface area surrounding the pits is called
land. The pits are arranged on spiral tracks; the pitch, or space between tracks on a DVD disc
is less than half the pitch between tracks on a CD, enabling more tracks to be placed on a DVD
disc. The laser in the DVD drive reads the pits, and then the drive interprets the information,
translating it into a signal that can, in turn, be used by a computer, television set, or audio receiver.
A DVD Primer: From DV to DVD
DVDs have greater capacity than CDs primarily because they use better laser technology. A
smaller spot of laser light, operating at a shorter wavelength, enables the DVD laser to read
smaller pits. The DVD laser also has the ability to change focus so it can scan and read multiple
layers.
To make it easier for the laser to focus on the smaller pits, DVDs are made from a thinner plastic
than what is used for CDs. A single thickness of DVD plastic, however, is too thin to withstand
handling and playing, so two discs are bonded together (whether or not they are single- or
double-sided), potentially doubling data storage capacity. Additionally, software used to read and
decode DVDs uses a more efficient method of error correction than CDs, leaving more room on
the disc for actual data.
Understanding DVD formats
Just as in digital video, where the term format may be used to refer to a variety of different
things, such as tape formats, broadcast formats, aspect ratios, or even content formats, in DVD
technology the term format also refers to different sets of characteristics, sometimes known as
technology layers. A technology layer is defined by a format. With DVD technology, we are primarily interested in two layers: the physical layer, which determines the recordability of a DVD,
and the application layer, which governs how the data is stored on a disc and how it is played.
Physical layer
The physical layer determines recording capability:
•Read-only format: DVD-ROM, with its large data storage capacity, is perfect for delivering
copyright-protected content such as movies and music, as well as multimedia and interactive
applications like video games, and training materials.
•Recordable formats: DVD-R and DVD+R have a storage format similar to CD-R and CD+R.
DVD-R and DVD+R discs can only be written to once, with the data recorded sequentially.
There are two types of DVD-R:
DVD-R(A) or DVD-R for Authoring, is aimed at the professional market and can be used to
generate masters for production recording.
➤
DVD-R(G) or DVD-R for General, was developed for the consumer market.
CD: Wider pitch, larger pits DVD: Narrower pitch,
smaller pits
D isc
st o r ag e
capacities
D isc T y pe
Number
o f sides
L ay e r s
pe r
side
Stor age
capacit y
Hours
of
vide o
CD
1
1
650MB
-
DVD-5
1
1
4.7 GB
2
DVD-9
1
2
8.5 GB
4
DVD-10
2
1
9.4GB
4.5
DVD-14
2
2, 1
12.32GB
6.5
DVD-18
2
2
17GB
8
The chart above indicates the capacity possible when
using the very best equipment and methodology.
Compression techniques and variable bit rate
(VBR) encoding can help you fit more data on a DVD,
as you’ll see later in this primer.
A note regarding the actual storage capacity of discs
The capacity of a single-layer DVD is often listed as
4.7GB, while the capacity of a CD is listed as 650MB. In
actuality, a single layer of DVD holds 4.7 billion bytes
(also known as Gbytes or GB), which is only 4.37GB. A
CD-ROM holds 650 million bytes—really only 635MB.
➤
D V D T E C H N O L OGY
A
P
P
L
I
C
A
T
I
O
N
L
A
Y
E
R
Multimedia
Movies
Music
P
H
Y
S
I
C
A
L
L
A
Y
E
R
DVD-Video
DVD-Audio
Read-only
DVD-ROM
Recordable
DVD-R
DVD+R
Rewritable
DVD-RAM
DVD-RW
DVD+RW
DVD-ROM
The application and physical layers of the DVD format
The authoring and general formats use different recording laser wavelengths, so they cannot be
written interchangeably by the same devices. They can, however, both be read by DVD players or
drives that support DVD-R media.
DVD+R uses a different technology approach and so may offer some advantages over DVD-R
depending on your needs. However, DVD-R(A) is still one of the most compatible formats available and the choice of many DVD professionals.
•Rewritable formats: The three variations of the rewritable format—DVD-RAM, DVD-RW, and
DVD+RW—can be written to, erased, and rewritten, over and over again.
A DVD Primer: From DV to DVD
DVD-RAM, the first rewritable DVD format brought to market could, in its infancy, only be
written while in a special cartridge because even a fingerprint left on the disc surface before
writing would cause errors. Double-sided DVD-RAM discs came in sealed cartridges, which
meant they couldn’t even be inserted into standard DVD-ROM drives. But DVD-RAM technology is evolving rapidly, becoming more and more compatible. DVD-RAM writers can
now also write to DVD-R and DVD-RW discs.
➤
DVD-RW (formerly known as DVD-ER and DVD-R/W) eliminated the protective cartridge
that was at first required by DVD-RAM, making it compatible with the disc-loading mechanisms in DVD players and DVD-ROM drives. However, some DVD players and drives don’t
recognize DVD-RW discs.
➤
DVD+RW was (according to its advocates) designed to be compatible with most existing DVD
drives and players but has not proven to be a perfect solution to the compatibility issue.
While Minus-R (-R) and Minus-RW (-RW) are the recordable and rewritable formats supported by the DVD Forum, several manufacturers got together (including DVD Forum
co-founders Philips, Sony, and Thomson) to create and manufacture the Plus RW (+RW), and
later the Plus R (+R) formats. For more information, see www.dvdplusrw.org and
www.dvdplusrw.org/resources/docs/howitworks.pdf.
➤
None of the recordable or rewritable formats currently available are fully compatible with each
other or with legacy players and drives. Compatibility can vary with media quality, player tolerances, and handling. For more information on the compatibility of specific devices, see:
•www.dvdmadeeasy.com
•www.vcdhelp.com/dvdplayers.php
•www.dvdplusrw.org/Compatibility.asp
The industry is working with manufacturers on these compatibility issues. The DVD Forum has
developed a certification program that guarantees compatibility with DVD-R, DVD-RW, and
DVD-RAM for those devices displaying the DVD Multi logo. A DVD Multi player (most players
made today) can read all three formats; a DVD Multi writer can record all three formats.
THE NEXT GENERATION: HIGH DEFINITION DVD
There are currently two competing standards for high
definition DVD:
•HD-DVD Disc is promoted by the DVD Forum, which
defined the DVD specification we have today. The
DVD Forum has an extensive membership but the
HD-DVD specification is mainly being driven by
Toshiba and NEC. HD-DVDs will have a 15GB capacity
per layer-per side, and an impressive 60GB capacity
for a dual-layer, double-sided disc.
•Blu-ray Disc is the name of the High Definition
(HD) format being developed by the Blu-ray Disc
Association (BDA), whose members include LG,
Panasonic, Philips, Pioneer, Hitachi, Mitsubishi,
Samsung, Sharp, Sony, and Thomson. Blu-ray Disc
(BD) will require significant changes to production
and replication equipment. Blu-ray Discs will hold
25GB per layer (50GB for a dual-layer disc).
Will high definition DVDs make standard DVDs
obsolete?
HD discs will not play on existing players, although
HD-DVD discs could play on computer DVD drives
with the right software upgrades. HD players will read
existing DVDs in addition to HD discs, so you won’t
have to replace your whole collection.
Application layer
The application layer defines how data is stored on the disc, and how it is played in a DVD player
or computer drive. Not all DVDs contain application layers—only those that must include a
system for navigating and playing the content on the DVD.
The DVD-ROM format is both a physical layer format and an application layer format. The application format, based on the Universal Disc Format (UDF) file system for optical media, is the
foundation of the application layer. Some portion of what is recorded on every DVD is in the
pure DVD-ROM format.
DVD-Video and DVD-Audio each define a more restricted logical format made up of video or
audio (or both) format specifications, interactivity, and other rules including file-naming conventions. DVD-Video and DVD-Audio files must be placed in special folders within the DVDROM directory, called VIDEO-TS and AUDIO-TS, respectively. You don’t need to understand all
the nuances of DVD file structures to create DVDs; your DVD authoring application will create
valid DVD volume and file structures for you.
Any or all of the three application formats—DVD-ROM, DVD-Video, and DVD-Audio—can
be stored on any of the three physical formats (with some variations). But, not all application
formats can be played back on all devices.
• DVD-ROM has significantly larger capacity and achieves higher speed data retrieval than the
CD-ROM application layer, making it an excellent medium for video games and other multimedia applications. For the most part, the DVD-ROM application format can only be played
back by computer DVD drives. There are some proprietary DVD-ROM application formats
that may only be played back by specialized devices (for example, video game platforms, like
Sony PlayStation, Xbox, and Nintendo GameCube).
A DVD Primer: From DV to DVD
Note: Don’t confuse the application format with the physical format—remember that DVD-ROM
discs (the physical format) can have any or all of the three application formats recorded on them,
and are compatible with most any DVD device; it is the application format, DVD-ROM, that can
only be played back on computers or other specialized devices.
• DVD-Video, often referred to as DVD, provides excellent picture and sound quality, as well as
the functionality needed to support interactive entertainment. With capabilities far superior
to VHS, DVD-Video offers broadcast-quality video and can provide better-than-CD-quality
audio. But, the methods used in content creation and reproduction can diminish the ideal.
DVD-Video uses MPEG-2 compression, a method that may result in occasionally noticeable
artifacts. These artifacts occur when backgrounds are complex or scenes change quickly, but
more often when the compression process is not performed optimally. As MPEG encoding
technology evolves, and as technicians acquire better compression skills, generally accepted
levels of quality for DVD-Video are rising.
The quality of the audio portion of DVD-Video is similarly dependent upon the quality of the
original material and how well it is processed and encoded. Capable of higher sampling sizes
and rates than audio CD, DVD-Video offers the potential for superb sound quality. The audio
for most prerecorded movies available on DVDs typically takes advantage of multichannel
surround sound using Dolby Digital or Digital Theater Systems (DTS) audio compression
similar to the cinema sound formats used in theaters.
DVD-Video discs can be played by DVD players and computer drives, although some incompatibilities may occur depending on the physical format.
• DVD-Audio is a separate specification that was initially intended to replace CD as the standard
distribution medium for music. DVD-Audio offers even higher quality audio than DVD-Video.
However, the format is not yet widely accepted. With somewhere over 700 DVD-Audio titles
available, it is at most a niche audiophile format, in part because DVD-Audio is not often found
in combination with DVD-Video on major motion picture releases. For the broad consumer
market, moreover, music has been moving towards portable, simple devices that store digitized
music at a somewhat lower quality.
DVD-Video
The DVD-Video format accommodates all of the following features:
•MPEG-2: The format accommodates MPEG-2 compression for video in either constant bit rate
(CBR) or variable bit rate (VBR). Audio can be uncompressed or use MPEG, Dolby Digital,
DTS, or ATRAC compression.
•Multiple audio tracks: Up to eight tracks of digital audio may be associated with a video track to
accommodate multiple languages or DVS, for example. Each audio track may have as many as
eight channels and can be in one of five formats: Dolby Digital, MPEG-2 audio, PCM, DTS, or
SDDS (Sony Dynamic Digital Sound).
•A choice of aspect ratios and formats: With fullscreen (4:3), widescreen (16:9), and pan-and-scan.
•Multiple video tracks: Up to nine different video tracks, also known as camera angles are
typically used for different viewpoints. (For example, you can have a view of an entire concert
orchestra as well as a close-up on the soloist.)
Descriptive Video Service
DVS (Descriptive Video Service) is a national service
(in the U.S.) that makes visual media accessible to
people who are blind or visually impaired.
A DVS audio track on a DVD describes key visual elements such as action, costumes, gestures, and scene
changes. Descriptive narration is carefully crafted
and applied so as not to interfere with the program
dialogue or original soundtrack.
•Subpictures: These allow up to 32 subtitle sets for multilingual or other titling options, in addition to Closed Captioning.
•Interactivity: Made possible by automatic seamless branching of video for varying story lines or
audience ratings (such as R or PG).
•Menus and special features: These facilitate interactivity such as random navigation when
video is chapterized, as well as edutainment opportunities such as Q&A, multiple-choice, and
true/false quizzes.
A DVD Primer: From DV to DVD
•Region coding: Limits playback to devices purchased in the same region as a way to control
distribution.
•Built-in content protection: A number of built-in schemes can be used to help prevent content
from being copied or altered. Region coding limits playback to certain areas of the world.
Not every DVD takes advantage of all the possible features. When you create your own DVD
content, you can choose which features to incorporate.
The remainder of this paper focuses primarily on the DVD-Video format and the basic information you need to produce content for and create DVDs that run in a standard DVD-Video player
or computer DVD drive that supports DVD-Video. To learn more about digital video, see the
Adobe Digital Video Primer from the Adobe website at
www.adobe.com/motion/events/pdfs/dvprimer.pdf.
Video compression
A single layer of a DVD can hold up to 4.7GB, but it takes more than 1.5GB for just a minute of
broadcast quality video at full resolution and frame rate. How can you fit a two-hour movie on
a single-layer, single-sided disc that has only enough capacity for about three minutes? It’s all
accomplished with the magic of video compression, and the evolution of the technology used was
so significant, it was awarded an Emmy.
What is compression?
In order to conserve storage space, as well as to make data easier to convey and process, the
amount of digital information needed for video is reduced or compressed before being recorded
onto DVDs. DVD players then decompress the data for playback.
Compression is a form of encoding, but not all encoding is compression. Compression and
decompression is handled by a codec which is an acronym for compressor/decompressor or
coder/decoder. The compression process is often part of the encoding process, but encoding may
encompass more than just compression. For example, the process of encoding DVD-Video may
also include adding Content Protection.
Codecs are found in hardware and software. A codec is a set of algorithms or computer code that
is specifically designed to compress and decompress video or audio information. A codec may be
hardwired into a circuit, as is the case in DVD players and on some video capture cards. A codec
might also be entirely software-based. You may be familiar with software-based codecs available
in video editing software such as Adobe® Premiere® Pro. Adobe Encore® DVD software offers
integrated transcoding and can automatically convert source files to the MPEG-2 video and Dolby
Digital audio formats (you can manually adjust the settings to optimize your DVD compression).
Different types of codecs have been developed to handle different types of tasks. Some codecs
are better than others for compressing and decompressing video during the editing process and
some are better suited than others for streaming video across networks. Some codecs are fine for
use in consumer video camcorders, while professionals might prefer equipment based on others.
Data compressed by a specific type of codec can only be decompressed by that same type of codec.
The DVD specification calls for MPEG compression—currently either MPEG-1 or MPEG-2,
although MPEG-2 is typically employed.
Making video fit into less storage space isn’t the only reason to compress it. At a hefty 1MB per
frame, uncompressed broadcast-quality video would have to be read and processed at a rate of
approximately 30MB per second, assuming the 29.97 fps (frames per second) rate of NTSC
(National Television Standards Committee), to be displayed in real time. If we convert the
more familiar storage units (megabytes) into standard shipment units (megabits) by multiplying by 8 bits for every byte, the result is a rate of approximately 240 Mbps (megabits per second).
However, DVD technology can retrieve information at a maximum rate of only 10.08 Mbps. So,
in addition to economizing on storage space, compression also reduces the data rate so that the
video can be read from the disk in real time.
If you would like to learn more about the basics of video compression, see the Adobe Digital
Video Primer on the Adobe website at www.adobe.com/motion/events/pdfs/dvprimer.pdf.
A DVD Primer: From DV to DVD
MPEG
MPEG stands for the Moving Pictures Expert Group, a working group of ISO (International
Organization for Standardization) and IEC (International Electrotechnical Commission) members responsible for the development of standards related to the coded representation of digital
video and audio. Among other initiatives, the film, video, and music industry professionals who
make up the MPEG define the specifications for several video encoding formats that include
compression and other features:
• MPEG-1, when used in DVD-video, is limited to a frame size of 352 x 480 pixels (NTSC) or 352
x 576 pixels (PAL) and a fixed data rate of 1.15 Mbps. MPEG-1 was the first MPEG standard
established and is still used for CD-ROMs, video CD (VCD), and some web video. It can be
(but is only occasionally) used for DVD-video.
• MPEG-2 has gained wide acceptance in the marketplace, and is the format most often used for
DVD, as well as for satellite and cable television transmission. MPEG-2 can provide extremely
high-quality video with frame sizes up to 720 x 480 pixels (NTSC) or 720 x 576 pixels (PAL).
Readily supporting data rates in excess of 8 Mbps (equivalent to 1MB per second), MPEG-2 is
ideal for DVD.
• MPEG-3 was abandoned as the industry moved on to complete MPEG-4. (Note that MP3—
which stands for MPEG-1, Layer 3—is an audio-only compression format and should not be
confused with MPEG video formats. MP3 audio files, or MP3s as they are popularly known,
may be saved onto DVDs, but not all DVD players will play them).
• MPEG-4 was developed to facilitate streaming video on the web and over wireless networks, as
well as providing mechanisms for multimedia interactivity. However, MPEG-4 has never lived
up to its expectations and has mostly been superceded by newer codecs such as H.264 and VC-1.
MPEG-2
The MPEG-2 video format includes a sophisticated codec that performs both intraframe (also
called spatial) compression and interframe (also called temporal) compression.
Intraframe compression basically reduces the amount of data within individual frames by
removing color information that is undetectable by the human eye.
Interframe compression reduces the amount of data by replacing parts of some frames with
mathematical predictions or interpolations, based on preceding and (sometimes) following
frames.
MPEG-2 generates three different types of frames for interframe compression:
•I frames (which serve as the keyframes in MPEG-2) use intraframe compression to reduce the
amount of image information within the frame through color sampling, among other means.
I frames contain a complete image.
•P frames are predictive frames, and may require less than a tenth of the data needed for I frames,
because they contain only the image information that is different from the previous frame.
•B frames, or bi-directional frames, contain only the image information that is different from
previous and subsequent frames. B frames can be smaller than P frames.
Interframe compression (bottom) uses B and P frames, which contain only those portions of the image that are
different from the adjacent frames. I frames contain complete images.
A DVD Primer: From DV to DVD
A typical MPEG-2 frame sequence might proceed like this:
IBBPBBPBBPBBPPB
Each sequence in MPEG compression is called a Group of Pictures (GOP). In the DVD-Video
format, each GOP is limited to 18 frames for NTSC and 15 frames for PAL.
How each frame is compressed depends on the type of content. If the content is fairly static—for
example, a talking head shot against a plain, still background—where not much changes from
frame to frame, then few I frames are needed, and the video can be compressed into a relatively
small amount of data. But if the content is action oriented—for example, a soccer game, where
either the action or the background moves or changes rapidly or dramatically from frame to
frame—then a greater amount of data is needed to maintain good quality and, therefore, the
video cannot be compressed as much.
It is important to note that not all MPEG-2 codecs are the same. MPEG-2 is a set of standards
or specifications that must be met for the codec to qualify as MPEG-2 and for the encoding and
decoding sides of the process to work properly with other software. Codec developers are free to
choose how they want to implement the standards in the codec software they create. Some implementations are better than others. If all the standards requirements are met, content encoded
with a codec from one developer will render seamlessly on players using decoders from any
number of different developers. When selecting an MPEG-2 codec, keep in mind the codec used
for encoding has a more significant impact on the final product than the codec used to decode on
the player. As long as the standard continues to be MPEG-2, the decoder chip in players will not
need to change to yield better quality for video that has been compressed with better encoding
technology.
CBR and VBR
MPEG-2 can be encoded in either the CBR (Constant Bit Rate) or VBR (Variable Bit Rate)
mode. Which you choose depends on the length of your program and the nature of your content.
CBR yields a fixed, or constant, bit rate throughout the program. Meanwhile, the quality of the compressed video can vary. If you use CBR, it is important to select a high enough data rate to compress
all of the content well. The data rate should be based on the portions of the video that are the
most complex. If the data rate is too low, too much compression may be applied to portions of the program with lots of motion and change, causing the quality to degrade. Conversely, in those portions
of the program without much action, the compression may not be very efficient and result in wasted
bandwidth. CBR is fine, and often preferable, for short subjects and video that isn’t action-oriented.
VBR considers quality first, adjusting the data rate to yield an appropriate amount of compression, depending on the content. VBR may yield the same average data rate as CBR, but the actual
rate will vary from scene to scene. Less compression is applied (that is, more data is allocated) to
the more complex portions of the program, more compression (less data) to the simpler sequences.
A minimum and maximum allowable rate is specified, providing the guidelines needed to keep
the entire program to an acceptable size and data rate. When trying to fit a long program onto
a DVD disc, VBR can make the difference between success and having to choose a more costly
alternative.
The more features you want to include on your DVD, the more closely you need to keep track of
how the data is adding up. In addition to the video, you’ll need to consider the data rate of the
audio, at 192-448 Kbps per Dolby Digital stream, with up to eight streams supported; and the
rate of subtitles, at 41 Kbps per language or other track, with up to 32 tracks allowed. The math is
really easy, just take the maximum data transfer rate of 10.08 Mbps for DVD Video (that is, the
video, audio, and subtitles combined) and subtract the total of the audio and subtitle tracks, as
well as approximately 0.4 Mbps for headroom. What’s left is the maximum available data rate for
your most complex scenes. (Note that the maximum data transfer rate for video alone can be no
greater than 9.8 Mbps.)
If you are planning a complex project, plan ahead—and understand that sometimes compromises need to be made. Even on Hollywood-produced DVDs, the featurettes are often more highly
compressed than the main feature.
When vbr is called for
If the content planned for a DVD is short relative
to the disc capacity—under an hour for a DVD-5,
perhaps—there is no need for VBR (Variable Bit
Rate) encoding because the entire program will
fit, even if it is all encoded at the peak video bit
rate for DVD. If the content is long—two hours, for
example—the average rate would need to be cut
by half, to approximately 4 Mbps, in order to fit. But
complex scenes generally require at least 6 Mbps for
acceptable quality. VBR encoding allows bits to be
saved in the simpler scenes, such as a conversation
between two people shot against a relatively static
background, that may require no more than 2Mbps.
Saved bits can be reallocated to the more complex
scenes, such as those with lots of action.
BANDWIDTH MATH FOR DVD
To determine the data rate available for the video in
the most complex scenes on a DVD, subtract the data
rate for the audio and subtitle tracks, as well as a little
extra for headroom. For example:
Maximum DVD-Video transfer rate 10.08 Mbps
Headroom - 0.4
5.1-channel (surround) English soundtrack - 0.384
Two 2-channel (stereo) soundtracks in
French and Spanish, each 0.192 Mbps
Peak data rate available for video
- 0.384
8.912 Mbps
For more information, visit http://main.wgbh.org/
wgbhpages/mag/servkes/description.
A DVD Primer: From DV to DVD
Audio for DVD-Video
Digital audio for the DVD-Video format can produce extraordinary sound quality. Up to eight
audio streams, or soundtracks, can be delivered on a single disc, including different language
versions and DVS. DVD-Video can also deliver multiple audio coding formats on a single disc
for mono, stereo, and 5.1-channel surround sound. The number and types of streams that can be
combined is flexible, limited only by the disc’s capacity.
Digital audio basics
Basic principles underlying digital audio are similar to those on which digital imagery and,
therefore, digital video are based. Film and video work by stringing together still snapshots and
relying on persistence of vision to re-create the sense of continuous motion.
Similarly, digital audio takes audio snapshots, or samples of sound, thousands of times each second. The number of samples—that is, the sampling rate—is quoted in thousands of samples per
second, or kilohertz. For example, 44,100 samples per second would be represented as 44.1 kHz,
which is the sampling rate of an audio CD. The higher the sampling rate you use, the greater
accuracy you will get in digitally mapping the analog audio waveforms of the original sound.
The bit depth used for samples is also an important factor in determining the accuracy of digital
audio. Bit depth is the number of bits used to describe the amplitude of each sample. Because
bits are binary (that is, representing a value of 1 or 0), each bit added doubles the potential for
accuracy. At 16-bit depth, there are 65,536 levels available to describe the audio sample; at 24-bit
depth there are 16,777, 216 levels available.
The zones between these discrete levels are called quantizing intervals. When a sound falls between
levels—that is within a quantizing interval—it cannot be accurately represented and must be
approximated by rounding up or down to the nearest level. Such rounding is referred to as
quantization noise.
sweeten your audio with Adobe Encore DVD
Adobe Encore DVD makes preparing your audio
assets for DVD projects easier with automated transcoding presets for audio formats. You can convert audio source files to 48 kHz using the integrated sample
rate conversion capability. Adobe Encore DVD supports two channels of Dolby Digital audio encoding. If
you have 5.1 audio content encoded in Dolby Digital
or DTS format, Adobe Encore can use that too.
In summary, higher resolution leads to greater dynamic range: the dynamic range of 16-bit is 96
dB (decibels) and the dynamic range of 24-bit is 144 dB. In other words, a greater bit depth yields
a more accurate digital representation of the original, analog audio waveform.
When you multiply sampling rate by bit depth by the number of channels used (for example, 2 for
stereo; 6 for 5.1 surround), the result is the data rate—which is equivalent to the bandwidth needed
to deliver the audio. The maximum data rate of audio CD, for example, can be figured as follows:
44,100 (sampling rate) X 16 (bit depth) X 2 (stereo channels) = 1,411,200 bits per second (1.4 Mbps)
The digitized audio waveform, when uncompressed, is known as PCM, short for pulse code modulation. PCM may be linear or nonlinear. Linear PCM (LPCM), which may be used for DVD,
spreads values evenly across the range from highest to lowest. Nonlinear PCM uses a nonlinear
quantization curve to allocate values based on dynamic range.
Audio compression
In addition to uncompressed digital audio, DVD-Video supports four types of audio compression:
MPEG audio (both MPEG-1 and MPEG-2), Dolby Digital, DTS, and the ATRAC compression
format used by SDDS (for descriptions of these formats, see Audio formats for DVD-Video).
Humans notice loss of detail in what we hear much more than in what we see, so when encoding for DVD, less compression is applied to the audio than to the video. Because audio requires
so much less space, you might wonder why we would bother to compress it at all—but even the
small amount of space gained by compressing audio provides enough room to yield a significant
improvement in the quality of the video.
Video compression, as we have seen, uses two basic methods to reduce data:
•Perceptual (intraframe) compression removes irrelevant visual information (mostly color)
from individual frames that the human eye is incapable of perceiving or unlikely to perceive.
•Temporal (interframe) compression removes redundant information, from frame to frame.
A DVD Primer: From DV to DVD
In digital audio compression, blocks of samples are divided into frequency bands of equal or
varying widths, and these bands are analyzed to determine how the compression will be applied.
Audio compression uses similar methods to video compression:
•Perceptual coding removes audio information the human auditory system won’t perceive,
either because it is out of the range of our hearing or because it is masked. Masked sound is not
heard by the human auditory system because of much louder sounds occurring concurrently,
just prior to, or immediately following softer sounds.
•Channel reduction removes redundant audio information between channels, especially when
there are six or eight channels.
Audio formats for DVD-Video
MPEG-2, Dolby Digital, and linear PCM (LPCM) are the three primary audio formats supported
by DVD-Video. DTS and SDDS formats are supported by some players. DVD-Video for NTSC is
required to include at least one track of either Dolby Digital or LPCM audio; DVD-Video for PAL
must offer at least one track of Dolby Digital, MPEG, or PCM audio. Dolby Digital is currently
the format most widely used for audio on DVD-Video.
Linear PCM (LPCM) is the digital audio format used on most studio masters, as well as on audio
CDs. For DVD-Video, LPCM can be sampled at 48 or 96 kHz at up to 24 bits, but some DVD
players may subsample 96 kHz down to 48 and may not use all 20 or 24 bits.
Up to eight channels are available, but the number of available sample rates and bit depths may
be limited when you use five or more channels. The maximum bit rate is 6.144 Mbps. LPCM is
rarely used for DVD-Video because of the bandwidth needed for multichannel implementations.
However, tests indicate that the average listener is unable to tell the difference between uncompressed LPCM and MPEG-2 or Dolby Digital audio for DVD, which are usually compressed at
about 10:1.
MPEG-1 audio delivers either monophonic or stereophonic audio and can only be CBR. It divides
samples into frequency bands of equal widths, which is easier to implement but less accurate
than using variable widths. MPEG-1 offers three compression techniques, called layers. Layer II
is the only one of the three MPEG-1 formats specified for DVD. (Layer III, also known as MP3,
is the popular compression format for music distributed via the Internet and, although not supported in the DVD standard, some players will play MP3 files).
MPEG-2 audio allows VBR encoding to efficiently accommodate transient increases in signal
complexity; although, in practice, this can prove to be problematic in passages where video and
audio require simultaneous peaks, thereby pushing the combined data rate past the limit. It also
adds multiple channels to produce (with the use of extensions) 5.1- or even up to 7.1-channel
audio. Because MPEG-1 and -2 audio encoding for stereo is identical, MPEG-2 audio is backward
compatible with MPEG-1 decoders.
Dolby Digital was designed with consumer delivery in mind and has, thereby, achieved a lead
position in adoption over other multichannel systems. Most all DVDs offer a Dolby Digital
soundtrack, and there’s a Dolby Digital decoder built into virtually every DVD player, which
turns Dolby Digital into standard analog stereo audio that can be played back by most any type
of audio equipment including a standard TV. Dolby Digital audio compression, also known
as AC-3, enables frequency bands of varying widths that match the critical bands of human
hearing, resulting in smoother sound than what can be achieved by fixed-width schemes. Dolby
Digital also offers other features, such as dynamic range compression (DRC) and dialog normalization (DN) that allow volume levels to be tweaked by the listener to accommodate various
situations. Dolby Digital provides up to 5.1 channels of audio to create surround sound.
DTS is an optional format that was originally developed for theaters. A home-theater version
was developed that has become popular for DVD among audiophiles. DTS for DVD is usually
compressed at 6:1 or 3:1, and some listeners report that the quality is better than MPEG-2 or
Dolby Digital. But differences may only be perceptible for playback on very high-end audio systems. DTS requires a special decoder, either in the DVD player or in an external receiver. Dolby
Digital or PCM audio are required on NTSC discs, so all DTS DVDs also carry a Dolby Digital
soundtrack because PCM and DTS together don’t usually leave enough bandwidth for the video
encoding of a full-length movie.
DOLBY DISTINCTIONS
Dolby Digital is the audio format most commonly
employed for commercial applications of the DVDVideo format. Dolby Digital is not synonymous with
5.1 surround sound; it is a format that can be used for
mono, dual-mono, stereo, Dolby Surround or any of
eight different configurations including 5.1 surround.
Dolby Digital encodes each channel to produce discrete multichannel audio. Virtually every DVD player,
worldwide, has a built-in Dolby Digital decoder. If the
system does not support discrete multichannel audio,
the Dolby Digital decoder in the DVD player can
downmix multichannel audio to two channels.
Dolby Digital Surround EX can, with the appropriate
decoder installed in the system, extract an additional
matrix-encoded surround channel, known as the
back surround channel, to be sent to a speaker in the
center rear of the listening environment. In effect,
this can yield 6.1-channel surround sound. Listeners
with a 5.1 channel setup don’t lose the back surround
channel information; it remains mixed with the left
surround and right surround channels.
Mono
Stereo
Dolby Surround
5.1 Surround
Dolby sound mode icons may be used to describe
the audio configurations that a product supports.
The small squares show speaker placement.
Matrix encoding is the process of combining multiple channels into a standard, two-channel stereo
signal.
Dolby Surround is an audio-encoding technique that
uses matrix encoding to blend rear and center channels into a two-channel signal. Dolby Surround can
be played on any stereo or mono system to achieve
a psychoacoustic surround simulation. However,
when Dolby Surround is played back on a multichannel system that has a Dolby Surround decoder, the
left, right, and rear channels are separated and fed
to the designated speakers. If the playback device is
equipped with Dolby Pro-Logic, the center channel
is also extracted. The Dolby Surround technique can
be employed by analog audio, broadcast audio, PCM
audio, Dolby Digital, DTS, MP3, or virtually any audio
format.
Dolby Pro-Logic is the process of (and the processing circuit for) extracting the center and rear audio
surround channels from matrix-encoded audio. The
newer Dolby Pro-Logic II also processes the signals to
generate more of a 3D audio experience.
A DVD Primer: From DV to DVD
10
SDDS, an optional multichannel audio format for DVD, is based on a theatrical soundtrack
format that uses a type of compression called ATRAC. While SDDS is written into the DVD
specification, it is a professional format intended only for motion picture theaters. Its eightchannel configuration, with five loudspeakers behind the screen, is not intended for typical 5.1
channel home systems.
AU D I O
F OR M AT
S A M P L E R AT E
BIT DEPTH
CHANNELS
B I T R AT E
Linear PCM
48 or 96 kHz
16, 20, or 24 bits
from 1 to 8
6.144 Mbps maximum
MPEG Audio
48 kHz
16 or 20 bits
from 1 to 7.1
32 to 912 kbps (384 kbps normal
average)
Dolby Digital
48 kHz
up to 24 bits
from 1 to 5.1 (5.2 with
new DTS-ES—Digital
Surround ES)
64 to 448 kbps (384 or448 kbps
recommended for 5.1 channels)
DTS (Digital
Theater Systems)
48 kHz
up to 24 bits
from 1 to 5.1 (5.2 with
new DTS-ES—Digital
Surround ES}
64 to 1536 kbps (typical rates
of 754.5 and 1509.25 for 5.1
channels, and 377 or 754 for 2
channels)
SDDS (Sony
Dynamic Digital
Sound)
48 kHz
up to 24 bits
8 (in theaters)
up to 1280 kbps
A comparison of the audio formats available for DVD-Video
Karaoke mode
Karaoke mode allows for five channels: two for stereo left and right (L and R) that are typically
instrumental only, two optional vocal channels (V1 and V2) that may be used for harmonies,
and an optional melody (M) or guide (G) channel that can help the karaoke singer carry the
tune. Karaoke mode can only be fully implemented by DVD players with karaoke features for
mixing the recorded audio and microphone input. All five audio formats for DVD-video support
karaoke mode.
Aspect ratios
The aspect ratio is the width to height ratio of an image. The 35mm still photography film frames
on which motion picture film was originally based have a 4:3 (width:height) ratio, which is often
expressed as 1.33:1 or, simply, a 1.33 aspect ratio (multiplying the height by 1.33 yields the width).
Standard TV matches the Academy Aperture (4:3=1.33:1 or 1.37:1)
In 1927, the Academy of Motion Picture Arts and Sciences endorsed the 1.33 aspect ratio as the
industry standard and it came to be known as the Academy Aperture. In 1931, the Academy
Aperture was modified slightly to 1.37 to make room for a sound track. Until 1952, the 4:3 image area
aspect ratio was used almost exclusively to make movies and to determine the shape of theater
screens. When television was developed, existing camera lenses all used the 4:3 format, so the
same aspect ratio was chosen as the standard for the new broadcast medium.
Widescreen (scope) formats (1.66:1—2.76:1)
In the early l950s, the motion picture industry began to see television as a threat. In a frenzy
to ensure that audiences left their living rooms and kept going to movie theaters, all manner of
gimmicks were tried, from color and sound innovations to 3D. In fact, if it weren’t for the competition from black-and-white TV, it might have been much later before color was widely adopted
for movies. Color technology was available as early as 1906 but, despite a few classic films like
The Phantom of the Opera being shot in color in the 1920s, it was dismissed as too costly.
One crowd-pleaser that withstood the test of time was a wider aspect ratio. Widescreen offered
audiences a you-are-there experience of panoramic cinematography. Based on a technique
patented in the 1920s, Cinemascope was the first commercially successful widescreen format,
making its debut in 1953 with the film The Robe. To produce an aspect ratio of 2.35:1 without
having to manufacture special film, cameras, or projectors, special anamorphic lenses were used.
The anamorphic lens used on the camera for shooting widescreen squeezed the image width to
fit on standard 4:3 format film. To show the movie, another anamorphic lens, one that stretched
the image back to normal, was fitted to the projector. And, of course, this new extra-wide aspect
ratio required an extra-wide screen.
The yellow crop indicates the 1.33 (4:3) aspect ratio
of the standard camera lens, the classic Academy
Aperture, and TV. The red crop selects a widescreen,
or scope view, with a 2.35 aspect ratio.
Shot with an anamorphic lens, the widescreen (red)
crop shown above would look like this on film—
remember that film frames have a 1.33 aspect ratio, so
the widescreen image, with a wider aspect ratio, must
be squeezed to fit.
Projected through an anamorphic lens, the image
expands to look like this— exactly like the original
(red) crop above.
Shot with a standard 4:3 camera lens, the scene would
look like this—as indicated by the yellow crop in the top
illustration—perfect for standard television viewing.
Masking either the camera lens or the projected
image yields a similar widescreen look to using
anamorphic lenses, but the quality is not the same—
there is a loss in picture resolution.
A DVD Primer: From DV to DVD
11
The widest popular American film made was Ben Hur, with an aspect ratio of 2.76:1. A host of
copycat scope formats were introduced (Warnerscope, Technicscope, Panascope, and others),
but the prohibitive cost of the special anamorphic lenses needed for both shooting and projecting, as well as the exhibitor’s reliance on often unreliable projectionists to remember to attach the
special lens to the projector, meant anamorphic scope techniques were reserved only for the most
extravagant productions.
In the mid 1950s, someone realized that the scope effect could be achieved inexpensively without
anamorphic lenses by shooting standard film through a viewfinder marked with the desired wide
aspect ratio so the cinematographer could properly compose the shot. When the film was shown,
the top and bottom of the projected image were masked off by covering the projection lens with
a cheap cardboard matte. (The projector was simply slid back a few feet, so that the image would
not appear too small to fill the screen.) This technique, known as soft matte, was the manner by
which cost-effective scope films were made for many years, with aspect ratios ranging from 1.66
to 1.86. But exhibitors still had to rely on projectionists to attach the matte. If they forgot, the
occasional microphone boom or prop-man’s hand that went unnoticed by a cinematographer
focused on the widescreen image area might be seen at the top or bottom of the picture.
The seemingly obvious solution was a technique known as hard matte whereby a mask is applied
to the camera lens when shooting. This technique put the control back into the hands of directors.
It wasn’t long before the industry realized there was money to be made from repurposing film
content for TV and, more significantly, videotapes for sale and rent. But something had to be
done with all those films shot for widescreen, both anamorphic and hard matte, neither of which
were well-suited for viewing in TV’s 1.33 aspect ratio. There were four apparent choices:
1. Slice off the sides. Initially, the most
common solution was to simply cut out
a 4:3 section at the center of the frame,
because that is where most of the action
in a movie is. The prevailing notion was
that audiences wouldn’t really know what
they were missing.
2. Squeeze the image horizontally. When
the audience needed to view the complete width of the frame, the image was
squeezed horizontally. Typically, this
technique was done only for titles and
credits of higher-budget, extra-wide,
anamorphic productions.
Four ways to present widescreen on standard TV
1
Widescreen can be made to fit 4:3 TV by slicing off the
sides. The image fills the screen, but much of it is lost.
3
3. Pan-and-scan. Rather than uniformly
slicing off the sides of a frame, an editor
can decide the best crop, frame by frame,
using the pan-and-scan technique. Using
video editing software, the editor slides
With pan-and-scan, a video editor selects the “best”
a 4:3 mask around, frame-by-frame,
crop, by panning and/or zooming the widescreen,
frame-by-frame.
following the action. The editor chooses
where to pan (or even zoom) each frame,
selecting (in the editor’s opinion) the most
critical portion. When presented on a standard TV, pan-and-scan fills the screen. The choices
made by the editor should be an improvement over the simple slice-off-the-sides technique,
but all manner of alterations to the original widescreen material may occur, such as unintended cuts where the action switches rapidly from one side of the screen to the other.
2
By squeezing the image horizontally,
widescreen can be made to fit 4:3 TV, but
the picture, if shown this way, is distorted.
4
Letterbox preserves all the information in
the widescreen format, placing black bars
above and below the image.
4. Letterboxing. By simply placing black bars above and below the widescreen image to block
out the unused portions of a standard 4:3 television set, the widescreen aspect ratio is preserved, as it was originally intended to be viewed.
A DVD Primer: From DV to DVD
12
Aspect ratios and today’s motion pictures
Now, let’s fast forward to the 21st century. Projectors have been permanently fitted with a set
of mattes which, when selected, mask soft matte films for either 1.66 or the more common 1.85
widescreen aspect ratios. Most films are shot soft matte, with view-finders equipped with frame
indicators for both the standard 1.37 aperture and the selected widescreen aspect ratio, to help
the cinematographer design shots that will look good when displayed in either format. These are
the three most common formats:
•Flat is the new Academy standard, with an aspect ratio of 1.85:1. It is typically shot soft matte
making it easy to repurpose the production for standard TV.
•Scope is usually for higher budget features, with an aspect ratio of 2.35:1. It is shot anamorphically, then converted to widescreen in the lab when distribution prints are made rather than
exhibited using an anamorphic lens on the projector.
Scope (2.35:1)
Flat/Academy Standard (1.85:1)
Academy Aperture (1.37:1)
A comparison of film aspect ratios in the common
production formats
•4:3 is the classic Academy Aperture, typically used for made-for-TV features and often used for
animated features with an aspect ratio of 1.37:1.
Many animated features and some European films are in the 1.66 aspect ratio. Special wideformat films, requiring special cameras and projectors, have also found periods of vogue, most
notably 70mm (2.20:1) and IMAX, as well as the Super 35 format used by James Cameron for
The Abyss and Ron Howard for Apollo 13.
TV today
Television is going digital. But the transition is going to take some time. No one expects consumers to suddenly throw away all their old TVs and buy all new. And, despite the wide adoption of
digital television delivery via cable and to satellite, the programming is still, for the most part,
engineered for analog broadcast and viewing. Set-top boxes convert the digital signal back to the
analog NTSC standard (in the U.S). before sending the signal to the TV. The U.S. Government
has mandated a full conversion of U.S. television broadcasting to Digital TV (DTV) to make
better use of available bandwidth.
There are two types of DTV:
•Standard Definition Television (SDTV) is quite similar to standard DVD. It can have a 4:3 or
a 16:9 aspect ratio and has resolution roughly equivalent to a conventional analog signal (525
lines of vertical resolution for NTSC).
•High Definition Television (HDTV) offers the potential for approximately twice the horizontal
and vertical resolution of current analog (NTSC) television. When combined with the compulsory 16:9 widescreen format, HDTV can offer about five times as much visual information as
analog TV. HDTV also takes approximately five times more bandwidth to broadcast than SDTV.
Not all TV sets available on the market today are HDTV-capable or HDTV-ready, not even the
widescreen (16:9) TVs. But the sets that savvy consumers are buying today are, at least, SDTVready, meaning that they are equipped to accept a digital signal directly (although most also
include analog inputs). So, we can connect our DV camcorders, digital VCRs, and our DVD players to our new TV sets via IEEE 1394 or DVI to achieve a pristine, noiseless picture.
Aspect ratios and today’s TVs
Because DTV is designed for two different aspect ratios, so are TV sets:
• Fullscreen TV: In the first decade of the 21st century, the standard television set still has a 4:3
(1.33) aspect ratio, also known as fullscreen. (For the rest of this primer, we’ll refer to 4:3 TV
as fullscreen). It’s the perfect shape for viewing films shot in the classic Academy Aperture format, but not so good for scope. Scope is what widescreen films—flat, scope, or any aspect ratio
wider than 4:3—have come to be called whether or not they have been shot with anamorphic
techniques.
A DVD Primer: From DV to DVD
13
• Widescreen TV: Many consumers have, by now, purchased a widescreen TV, with a 16:9 (1.78)
aspect ratio. (For the rest of this primer, we’ll refer to 16:9 TV as widescreen). But, because
most broadcast TV and much of the video recorded on VHS, laserdisc, and DVD is fullscreen,
widescreen TVs can be programmed to display 4:3 in one of two ways. The first is pillarboxing
(also known as windowboxing) which electronically generates black or gray vertical bars to fill
the leftover space on the sides, or magnifying the picture to fill the 16:9 screen (but cutting off
the top and bottom of the picture to do so). Of course, the widescreen TV aspect ratio is much
better suited than fullscreen for displaying scope—its 16:9 (1.78) proportion is quite close to
the Academy Standard, or Flat, proportion of 1.85 in which most of today’s films are produced.
With even wider scope aspect ratios, a letterboxed picture fits into the widescreen shape much
better than it fits the fullscreen shape, with less vertical space above and below the image needing to be filled with black mattes. What’s more, widescreen TV is specifically engineered to
showcase anamorphic widescreen.
Aspect ratios and DVD: more choices for better or worse
With VHS and laserdisc, you got the version that was recorded. If the content was scope, it was
either made to fill the fullscreen TV aspect ratio by slicing off the ends or by using pan-and-scan
or it was rendered letterbox, with the black bars at the top and bottom of the image added in the
studio. When the bars are recorded as part of the image, the picture suffers from a loss of vertical
resolution—on fullscreen TVs and widescreen TVs alike—because a number of pixels must be
sacrificed to accommodate the matte bars. Widescreen TVs can be set to magnify studio-letterboxed
video to fill the screen, but this may reveal image defects too small to detect in the non-magnified
image, thus making the enlarged picture look worse.
To get the best picture possible on widescreen TVs, digital technology borrowed the anamorphic
concept from film. Digitized video stored on DVDs (or broadcast digitally, for that matter) can
be anamorphically squeezed. The widescreen TV pixels have a wide aspect ratio that effectively
unsqueezes anamorphic pictures. In fact, when a standard 4:3 picture is sent to a widescreen
TV, if the set is not configured properly to compensate for its wide pixels, the image display is
distorted, appearing to be fat.
For fullscreen TV, where the pixels have the traditional aspect ratio, anamorphically squeezed
video is unsqueezed by the DVD player (or set-top box, in the case of digital broadcast) before it
is sent to the display. When the DVD player unsqueezes anamorphic video for 4:3 display, it can
(depending on how the viewer chooses to set it up) either add black bars to the top and bottom to
letterbox the picture or it can allow the image height to fill the screen, in which case the sides of
the picture will be sliced off. Some DVD players can automtically pan-and-scan of anamorphic
video that includes special coding to indicate the optimal pan-and-scan center-of-interest offset.
But buyer beware! Anamorphic video, when displayed as a result of automatic letterbox or auto
pan-and-scan modes, can actually produce a worse-quality picture than prerecorded, studio-letterboxed or studio-pan-and-scan versions.
Many current DVDs are marked as Enhanced for Widescreen, Enhanced for 16:9 TVs, or Anamorphic, and most of these discs offer viewers two options: a studio-generated pan-and-scan
version on one side of the DVD disc to give viewers with fullscreen TVs the best quality picture,
and, on the other side, an anamorphic version designed to take advantage of widescreen TV.
Most current DVD players have four playback modes:
Fullscreen for the prerecorded, studio pan-and-scan version. If the viewer chooses to watch
the studio-generated pan-and-scan version, the DVD player decodes the picture and delivers
the signal to the display for playback. On a fullscreen TV, the picture fills the screen. A wide­
screen TV can be set up to either pillarbox the image by placing black bars on the sides or
to magnify the image to fill the screen. But magnification results in loss of even more of the
picture at top and bottom than has already been cropped for fitting into the 4:3 aspect ratio.
Magnification may also reveal imperfections that might not be noticed otherwise.
➤
Fullscreen TV has a 4:3 (1.33)
aspect ratio—4 units wide by
3 units high
Widecsreen TV has a 16:9 (1.78) aspect
ratio—16 units wide by 9 units high
THE KEY TO ANAMORPHIC VIDEO
Studio letterboxed video includes black bars in each
frame of video stored on the DVD. Anamorphic video
does not. Why is this so important? Each video frame
stored on a DVD is made up of 720 x 480 pixels. If, as
is the case for video that is letterboxed prior to being
recorded, 25% of the available pixels are used up for
black bars at the top and bottom of the widescreen
image, there are fewer pixels available to store the
actual video information.
Anamorphic video, on the other hand, uses all available pixels to store as much video information as
possible. Every one of those 720 x 480 pixels carries
video information. You can think of a widescreen
TV as acting like an anamorphic lens. If you watch
anamorphic video on a standard 4:3 TV, it will appear
tall and fat but it will fill up the entire screen; which
is how it is actually recorded on the DVD. If you play
this same content on a widescreen (16:9) TV, the TV
itself is wider and it stretches the image to the correct
proportions.
When a DVD player decodes anamorphic video for
fullscreen (4:3) TV, it unsqueezes the image and
generates the black bars electronically. When a
widescreen TV displays anamorphic video, the wide
pixels effectively unsqueeze the image. In either case,
more video information—which equates to higher
video resolution—is available in the signal sent to the
display. Thus, when anamorphic video is displayed,
the picture has better resolution than studio-letterboxed video.
A DVD Primer: From DV to DVD
14
Auto letterbox for 4:3: The DVD player
stretches the anamorphic video back to its
original scope aspect ratio and generates
matte bars at the top and bottom of the
picture. Together, the black bars at top and
bottom take up nearly 25% of the usable
scan lines, leaving only about 75% of them
to draw the image. To compensate, a letter­
box filter in the DVD player combines
every four lines into three either by simply
dropping out every fourth line or by using
weighted averaging to combine lines. So,
even though the anamorphic video has
higher resolution to begin with than studioletterboxed video, it does not make the
best use of all the available information.
Often, scope video letterboxed by high-end
studio equipment, and prerecorded on laserdisc or DVD, produces a better picture
than auto-letterboxed anamorphic video
when displayed on a fullscreen TV.
➤
Auto pan-and-scan: The DVD player
stretches the anamorphic video back to
its original widescreen aspect ratio, but
cuts off the sides according to a center of
interest offset specified for each frame
when the video was encoded. Unlike
studio pan-and-scan, where the editor can
pan from side to side, zoom, or both, to
crop the very best portion of the image,
auto pan-and-scan only travels laterally and must include the full height of
the widescreen frame. Moreover, when
studio pan-and-scan is recorded on DVD,
the entire allotment of 720 x 480 pixels
is dedicated to the cropped frame, while
auto pan-and-scan may delete upwards
of 25% of the video’s width. That means
that 720 pixels across might be reduced to
540 pixels, resulting in a significant loss
in horizontal resolution. While the loss in
resolution might not be too noticeable on
a fullscreen TV, if the picture is magnified
on a widescreen TV, the loss in resolution
can become distinctly noticeable. And,
just as when any 4:3 picture is magnified
to fill the width of the widescreen TV, the
image—which has already been cropped
horizontally—will be cropped vertically, as
well. Generally, the studio pan-and-scan
version prerecorded on the other side of
the DVD results in better picture quality
on fullscreen and widescreen TVs. Therefore, not many DVDs are implementing
auto pan-and-scan.
➤
Academy Aperture (1.33:1) fits fullscreen TV
perfectly, because television was originally
based on the classic 4:3 film format.
When Academy Aperture is displayed on widescreen
TV, the set generates sidebars to pillarbox (or windowbox) the picture.
Academy Standard, also called flat at (1.85)
looks like this when letterboxed on fullscreen.
1.85 fits widescreen TV just about perfectly because
the aspect ratios are very similar.
Wider Scope, for example, 2.35:1, looks like
this when letterboxed on fullscreen TV.
When 2.35 is displayed on widescreen TV, the image is
maximized; the matte is minimized.
Scope, when recorded for 4:3, or auto panand-scanned, looks like this on fullscreen.
If magnified (instead of pillarboxed), the top and
bottom of 4:3 or auto pan-and-scan are cut off.
Anamorphic displayed on an improperly set
up fullscreen system may look like this.
4:3 video displayed on an improperly set up widescreen system may look like this.
A DVD Primer: From DV to DVD
15
Auto widescreen: The DVD player decodes and sends the anamorphically squeezed video to
the display; the wider aspect ratio of the widescreen TV’s pixels effectively unsqueezes the
picture. Auto widescreen fulfills the promise of anamorphic DVD. Academy Standard films,
with their near-16:9 aspect ratio, use every available pixel for image information, and every
pixel recorded is displayed, resulting in a stunningly clean, clear picture. Scope pictures that
have wider aspect ratios are studio-letterboxed before the anamorphic video is recorded on
DVD, so, while there is some loss in vertical resolution, it is minimal—the matte bars at the
top and bottom of the picture are often so narrow as to hardly be noticeable.
➤
Pixel aspect ratios
Analog PAL and NTSC video signals have a fixed vertical resolution, which can be measured by
the number of scan lines on the screen. However, the horizontal resolution of an analog video
signal is really only limited by the bandwidth of the camera and recording device. Most studio
cameras have very good horizontal resolution, much higher than the equivalent vertical resolution specified by the video format.
When digital video standards were standardized in the late 70s and early 80s, it was thought that,
in order for a video signal to look good and to capture the true resolution of the cameras, the
horizontal resolution had to be higher than the vertical resolution. A standard of 720 pixels was
agreed upon for a number of reasons, but mostly because the same sample rate could be applied
to both PAL and NTSC video formats. Out of the 720 pixels, only 704 are defined to be in the
active picture area. The extra 8 pixels on each side of the image can have video in them, or they
may be blanked in the camera (that is, just black is recorded).
If you compute the aspect ratio of a frame that is 704 pixels wide by 480 pixels high (the geometry of a standard video signal), you do not get 4:3. Four divided by three is 1.333 (the standard
video image aspect ratio), and that figure multiplied by 480 lines high works out to a width of
only 640 pixels. Digitized NTSC and PAL video squeezes in more pixels per horizontal line by
using nonsquare pixels, in this case, pixels that are slightly narrower than standard square pixels.
Computers typically use square pixels, and until recent years, most programs did not handle
nonsquare pixels very well.
The pixel aspect ratio of video is the image aspect ratio (1.333) times the horizontal size (480 for
NTSC based video) divided by the vertical size (remember to use 704, not 720), which equals
a pixel aspect ratio of .909 (usually just specified as .9 in the user interface of most authoring
programs, but the correct value is actually applied to the video). Since there are more pixels
horizontally than there are vertically, the pixels are taller than they are wide. If you produce your
video anamorphically for best image quality, the pixels are taller than they are wide, with a PAR
of 1.2.
All DVDs use nonsquare pixels, and if you produce your DVD with improper settings, the image
will not look right.
Aspect ratios and your DVDs
Most television viewers will move to DTV during the next decade; many videophiles have already done so. Many digital video camcorders enable you to switch between standard 4:3 aspect
ratio (Academy Aperture) and 16:9 (widescreen) aspect ratio. The less expensive of these adjustable camcorders simply lop off the top and bottom of the image, using only 75% of the scan lines
to create the widescreen effect, and resulting in lower vertical resolution. Some more expensive,
professional-grade DV camcorders can be fitted with an anamorphic lens. But, if you don’t have
access to that kind of equipment, you’ll find some tips for shooting the best widescreen possible—
with affordable equipment—in the How do I make a DVD? section of this primer.
Progressive scan DVDs
Content shot with video cameras is typically interlaced content—half the image is scanned by
skipping every other line (one field), and then the image is filled in with the second field. Content
shot on film, on the other hand, uses progressive scanning when transferred from film to video.
Unfortunately, the frame rate of film is 24 frames per second, which is different from the video
frame rate of 25 frames per second for PAL and 30 (technically 29.97) frames per second for NTSC.
A DVD Primer: From DV to DVD
16
The process of transferring film to video and the expensive machine used to do it are both called
telecine. The telecine is basically a projector that projects film directly onto a video sensor. When
film content is transferred to PAL, the film is just run at 25 frames per second (a 4% speed increase)
and each frame of film is exactly mapped to a frame of video. However, when film content is
transferred to NTSC, a process known as 3:2 pulldown is used. Each frame of film is scanned so
that it is mapped to three fields of video for the first frame of film, then two fields of video for the
next frame of film. This sequence then repeats throughout the capture process. The result is that
the video plays back with an uneven look to it.
If you encode the video with this 3:2 pattern, your results will not be optimal. The 3:2 pattern
confuses the motion estimation algorithms in the codec. It sees the video as constantly speeding
up and slowing down, making the encoding less efficient and increasing artifacts in the video.
Secondly, you are encoding 20% more data, as the telecine process adds redundant fields that
need to be encoded into the video stream. Finally, you are encoding interlace content, which does
not encode as efficiently as progressive content.
The solution? Put the video through an inverse telecine algorithm before encoding the video for
your DVD. This process removes the 3:2 pattern so that you can encode the 24 fps progressive
frames just as the content was originally shot.
On playback, the DVD player will do one of two things: If the viewer has a DVD with a progressive scan mode and a TV that can take the progressive scan video input, the video will be shown
in its native progressive format, also known as 480P (the best way to view DVDs). Otherwise, the
DVD player itself will reinsert the 3:2 pattern before the video is sent out as standard NTSC or
S-Video to the TV (still better than encoding the 3:2 pattern on the disc).
PIXEL ASPECT RATIOS
Even individual pixels have an aspect ratio! Square
pixels, like those typically used in graphics programs
such as Adobe Illustrator® and Adobe Photoshop®*
have a 1.0 pixel aspect ratio. But video images are
made up of nonsquare pixels, the aspect ratio of
which varies from format to format.
Some common formats and their corresponding pixel
aspect ratios:
D1/DV NTSC 0.9
D1/DV NTSC widescreen 1.2
D1/DV PAL 1.066
D1/DV PAL widescreen 1.4222
Anamorphic 2:1 (film transfer) 2.0
Adobe Encore DVD automatically scales square-pixel
graphics to fit the proper nonsquare pixel aspect ratio,
so your images won’t look squashed when viewed in
a video format.
*Photoshop 7.0 and earlier supports only square pixels,
but Photoshop CS and later allow you to work directly
in nonsquare pixels so no conversion is necessary.
Almost all movies sold on DVD today are produced with progressive scan encoding.
24P video
Producing content with 24 fps progressive scan used to be the domain of film producers, but
many newer high end camcorders have a 24P mode. High-definition video is also a large source
of progressively scanned material that is originated on video rather than film. If you have the
right equipment, shooting your material in 24P anamorphic 16:9 will produce the best results.
Multiple camera angles
The DVD-Video specification offers up to nine different camera angles. Angles are different
views of the same scene, shot by different cameras. They are recorded as different video tracks of
the same length and associated with the same audio tracks.
The promise
The multiple camera angle feature was intended to offer audiences interactive choices to enrich
the entertainment experience. The video recorded simultaneously by multiple cameras can be
stored on the single DVD and give the viewer choices. For example, the viewer might first watch
a high-speed chase scene that is edited for dramatic effect in a film. But the second time around,
the viewer might select a view shot from a different point-of-view such as that of one of the drivers.
With multiple angles on a DVD, viewers could even switch back and forth between a full-stage
view and assorted angles of individual performances.
The reality
Not many commercial DVDs actually take advantage of this multiangle capability because it
takes more work to produce and consumes more disc space.
The possibilities
This multiangle capability offers many possibilities:
•A how-to DVD might show the construction, assembly, or maintenance of a complex piece of
equipment from several different angles.
•A training DVD could instruct retail or restaurant employees about an in-store situation from
the perspective of a sales associate, a store manager, or customer.
A DVD Primer: From DV to DVD
17
•A wedding ceremony might be seen as viewed by the guests, through a close-up of the bride’s or
groom’s face, or from numerous angles that have been artfully edited together.
•A sequence in a science lesson might describe a natural process, such as mitosis, with the option
to view either actual time-lapse video or an animated and annotated representation in the
place of an alternate camera angle.
Subpicture streams and closed captions
Subpictures laid in on top of background video or still images are typically used to provide
subtitles, karaoke lyrics, instructions, or other text. But subpictures are not limited to text only.
Because they are composed of bitmap graphics, they can include images of any shape. Subpictures are also used for highlighting menu items when they are selected or activated.
DVD-Video accommodates up to 32 discrete subpicture streams. Each subpicture stream is
synchronized with the video and audio streams and multiplexed into the overall DVD-Video
stream, so that it can be selectively turned on or off. Subpictures made up of of text, graphics,
or a combination of both can be partial- or fullscreen size up to 720 x 480 (NTSC) or 720 x 576
(PAL). Simple motion effects can be applied to subpictures so they appear to change on a frameby-frame basis, fade in and out, wipe in color or transparency, or scroll up and down.
What are subpictures made of?
While the DVD-Video format supports up to 32 simultaneous subpicture streams, the bandwidth allocation for each stream is quite limited. To meet the bandwidth restriction, subpicture
text and graphics are compressed with Run-Length Encoding (RLE). Run-length compression
is a form of lossless compression, so the original picture can be reconstructed with no loss of
detail. It is an excellent choice for subtitles and other text where legibility is critical. Run-length
compression uses the principles of spatial compression to remove redundant areas of information from within the frame. For an area that is all the same color, run-length compression stores
the color information for a single pixel, along with an instruction for how many times to repeat the
pixel. So, for an area of 100 pixels that are all the same color, instead of storing 100 pieces of data,
run-length compression only needs to store three pieces: a marker indicating a run of similar
colored pixels, the color, and the count.
Run-length compression is not very useful for compressing photographic images or detailed
illustrations that are made up of many colors because there would be little reduction of data. It
does, however, work very well on simple pictures made up of a limited number of colors. So, to
accommodate run-length compression, DVD limits subpictures to just four colors per frame,
selected from a fixed palette of 16 colors per program. This 16-color palette may be chosen from
the more than 11 million colors provided in the 24-bit color mode. The colors chosen should
also be NTSC-safe. The 16-color palette can change, from program to program or from menu
to menu, on the same DVD. Each pixel is represented by 2 bits, enabling four types: background
(BG); foreground (also known as pattern, P); emphasis 1 (El); and emphasis 2 (E2). Each pixel
type is associated with just one color, selected from the palette of 16, as well as just one transparency level from 0 (invisible) through 15 (opaque).
Original
oonnnoooooonnooonnnnnnoo
Encoded 2o 3n 6o 2n 3o 6n 2o
Run-length compression replaces redundant pixels
with a value indicating the number of times the pixels
are to be repeated.
While this all sounds pretty complicated, with most entry-level DVD authoring applications you
don’t even need to know this much to highlight menu buttons and create subtitles.
What’s the difference between subtitles, captions, and Closed Captions?
•Subtitles are usually a foreign-language translation of dialogue, but the term can refer to any
text that is superimposed over video or film, typically appearing at the bottom of the screen.
Subtitles may not include every utterance—for example, if a character in an action scene
simply shouts out a name (“Will Robinson!”), subtitling may be deemed unnecessary. Subtitles
do not, typically, identify the speaker, as they are not specifically intended to assist the hearing impaired; subtitles are typically intended for hearing people who do not understand the
language of the dialogue.
A DVD Primer: From DV to DVD
18
•Captions are almost always in the same language as the audio, although captions of a foreign
language translation may be made available. Captions are intended for deaf and hearingimpaired viewers. Ideally, captions impart every utterance and identify the speaker, either
by moving around the screen to appear in proximity to the speaker or by denoting, in the
text, who is speaking. Captions convey tone and type of voice, where necessary (for example,
[whispering], or [Russian accent]). Captions include descriptions of sound effects and other
significant audio—for example, thunderclap, music rising to crescendo, or sound of breaking
glass off-screen.
Captions may be supplied, like subtitles, as a subpicture stream, in which case they are called
open captions. To distinguish them from subtitles or Closed Captions, open captions are usually
referred to as captions for the hearing impaired. Like other subpicture streams, open captions are
multiplexed into the overall DVD Video stream and extracted into a discrete stream by the decoder
in the DVD player, so that they can be turned on or off at the viewer’s discretion, assuming the
DVD author makes this a choice.
•Closed Captions are not subpictures. They are made up of individual character codes carried in the MPEG-2 video stream and must be generated by a special encoder during the
post-production process. Closed Captions are not decoded by the DVD player. The display of
Closed Captions requires a special decoder chip which, by law, is built into every U.S. television
set (larger than 13”) sold since the mid-1990s. When the Closed Captions option is selected on
the television set, Closed Captions are displayed. Closed Captioning is an NTSC standard supported by the DVD-Video format. DVD does not, however, support PAL Teletext, the European
equivalent of Closed Captioning.
The Character panel in Adobe Encore DVD, where you
can format text typed directly on the screen or created
by running a script.
DVD-Video interactivity
We have become used to the kind of real-time and on-demand interactivity made possible via
Internet applications or application software delivered on a CD-ROM or in the DVD-ROM format—video-game play is a prime example. While DVD-Video can provide random access to all
of the content stored on the disc, enabling the viewer to jump to any defined point in a video in
less than one second, the interactivity afforded is comparatively limited.
DVD-Video can simulate searching and game scoring, but results cannot be generated or computed on the fly. All interactivity must be created entirely in production and stored on the DVD.
Seamless branching
A DVD-Video disc can be authored to allow the viewer to choose how a video program unfolds.
The possibilities are limited only by the imagination of the DVD author.
For example, the viewer might be given choices to skip or include certain scenes, experience an
alternate ending, view the director’s cut, or share a specific character’s point of view. Once selected
by the viewer, these choices are presented seamlessly (that is, without a break in the perceived
f low of the program). This seamless branching, also known as multistory capability, is a big
improvement over the branching functionality in earlier digital video formats. With laserdiscs
and videotape, the user has to interrupt the playback to jump to another part of the program.
An example of seamless branching
If the French-language version is selected,
the DVD not only plays the French-dubbed
soundtrack, but also jumps to French-language
visual sequences.
With DVD-Video, several levels of branching can be offered to the viewer. Some examples might
be long or short versions of a chase scene, or with or without a gory ending. Random branching
can keep the experience fresh with each subsequent viewing.
A DVD Primer: From DV to DVD
19
Seamless branching functionality can also offer alternative presentations played without the
viewer even realizing such a choice was made. For example, if an alternate language soundtrack
is selected, scenes in which written words appear on signage might be replaced with matching
language versions.
Due to the complexity of seamless branching and the difficulty in preparing content that uses the
feature, seamless branching is not used frequently. No commercially-available DVD authoring
systems currently offer the feature, and it has only been used on a handful of commerciallyavailable discs.
Parental management
A special parental menu (which is accessed differently on different DVD players) allows parents
to set passwords for specific rating levels (for example, any content rated R or NC-17).
There are three different implementations of parental management:
Adobe offers all the software you need to create
dynamic DVD menus: Illustrator and Photoshop for
designing backgrounds and graphic elements such as
buttons, Adobe After Effects® for developing motion
graphics for motion menus, and Adobe Encore DVD
for putting your menus together with creative authoring tools for professional DVD production.
• Lockout: If a disc with a rating above the established level is inserted in the player, it will not play.
• Censorship: If the content has been rated on a scene-by-scene basis, the ratings are included
in the encoding, and chapter points are set for multistory functionality, then the player can
map the rating against the content and skip over those scenes that are unacceptable. While the
playback will be seamless, the story line may suffer gaps in continuity.
• Multirated: Branching allows DVD-Video creators to create seamless playback of parentally
controlled content. Objectionable scenes are replaced by alternative ones. While this feature
is noteworthy for its ideals, the reality is that very few DVDs offer content variations for less
mature audiences. The added production expenses are prohibitive and generally include things
like: shooting extra footage, recording additional audio, editing the new sequences and submitting them for rating approvals, setting up branch points, and synchronizing the soundtrack
across the jumps. Furthermore, packaging standards have not yet been established for DVDs
with multirated content, so many video store chains don’t carry them.
Menus and navigation
The DVD-Video specification accommodates on-screen menus; it does not require them. But,
without menus, DVD is really nothing more than a storage and playback medium. Menus support the interactive features that make DVD such an appealing delivery vehicle for video. Most
viewers expect at least one menu that lets them jump directly to the content they want to view.
The infrastructure of DVD navigation
Navigation is a good example of how the various components of DVD technology work together
to deliver an interactive experience. The DVD-Video format stored on a DVD disc contains
presentation data (video, still image, and audio content) and navigation data (information and
commands that provide basic interactivity). The DVD player includes a presentation engine.
This engine uses the presentation data from the disc to control the content, and to provide a user
interface, including menus and other interactive features.
What is a menu?
A menu is a user interface (UI) that gives the viewer the ability to navigate through DVD content.
The graphical user interface (GUI) part of a menu typically consists of:
•a background that is either a still image or motion video (animation or live action). A menu
may also include background audio.
•informational and sometimes instructional text.
•buttons in the form of graphics, still photos, or thumbnail-size motion video that link to points
in the video content on the DVD or to other menus.
If the background or the buttons incorporate motion video or animation, the menu qualifies as a
motion menu.
A DVD Primer: From DV to DVD
20
The user moves between buttons on the menu by pressing the up, down, left, or right buttons
on the player’s remote control (either a physical device if the player is a set-top box or a virtual
controller if using a computer). A button can be highlighted in the GUI when selected. The user
presses the select button on the controller to activate the highlighted choice. If the DVD is being
played on a computer, a mouseover usually indicates a selection, causing the button to be highlighted. The user can click the mouse or press Enter to activate subpictures that may be used to
provide visual feedback—that is, to highlight menu choices—when buttons are selected, and then
when they are activated. Subpictures are the most common and most efficient way to highlight
menus, because the 24-bit-color background graphic remains the same, while only the RLEencoded subpictures change.
Action buttons (or action menus) are another method used to provide visual feedback (not
to be confused with motion menus). A highlighted action button is really a jump to an
entirely different 24-bit menu graphic—sometimes with motion. While this approach enables a
full palette of colors to be used for highlighting (as contrasted to the limitations of using subpictures), and can be used for more complex motion highlighting with dynamic effects, it may not
be optimal. Action buttons are more difficult to implement, the feedback may be quite slow on
some players, a mouseover on a computer player will usually not cause the highlight effect, and
they use more resources.
DVD player controllers (both physical and virtual) provide a select button and the up, down, left, and right
buttons for menu navigation. They also have buttons
that let the user play, pause, and stop the video; play
the video forward or backward at different rates; step
through the video frame-by-frame; skip over chapters
or jump to the beginning of the title; jump to the
title menu or root menu; control audio volume; and
choose language, subtitle, or camera angle options.
One form of the
Windows Media®
Player controller
for Microsoft®
Windows® XP
Top
Menu
Enter
DISC
Presentation data
Return
Navigation data
Stop
Play/Pause
/
PLAYER
Presentation engine
Navigation manager
REMOTE
CONTROL
VIDEO
AUDIO
Prev
Scan
Audio
Angle
Next
Subtitle
Typical layout of a DVD
player remote control
device
The Top button (which may
alternatively be labeled;
Title, Guide or lnfo) takes
the viewer to the very top
of the content hierarchy—
to the most primary table
of contents menu, which
is known as the title menu
or top menu. The Menu
button invokes a jump
to the most appropriate
menu, based on the current
state of the content display.
The Return button takes
the user to the next higher
level of the menu hierarchy.
Some software player
controllers don’t include buttons that are redundant
to mouse selection controls in order to minimize
screen real estate. Many software players can even
be configured in a variety of ways (for example, to be
invisible when a video is playing).
Navigation/presentation technology model
What can menus and buttons do?
Many menus simply facilitate choices between titles or chapters on the DVD. Some menus let the
user choose the way in which the content is presented. This is generally how the viewer chooses
audio and language selections, whether or not to have subtitles or captions, and—if multistory
options are available—which scenes will be included. A menu can masquerade as a quiz—the answer
selected, once activated, will determine the next jump. Choose correctly and you’ve chosen to
play a still or video sequence that congratulates you on your aptitude; choose incorrectly and
you’ll view content that may suggest you try again, or will provide more information.
Each button must be programmed to perform a desired function—in most cases, to jump to a
specific point in the video content, or to another menu. So there needs to be a system for identifying desired points in the video content, as well as recognizing the menus and subpictures that
need to be displayed upon command—a road map, of sorts.
A DVD Primer: From DV to DVD
21
Content hierarchy—the DVD road map
The video content saved in the DVD-Video format and stored on the disc can be parsed much
like a map. In other words, it can be broken down into hierarchical units. Further, the dividing
lines between these map units are indicated by specific conventions we recognize—solid or broken
lines of varying weights and colors. Just as with maps, it helps to understand the nomenclature
used to describe DVD-Video content, and the hierarchy of menus and buttons. And, just as with
maps, the DVD-Video hierarchy is flexible, so it can be quite confusing to the newcomer. Entrylevel and even quite advanced DVD authoring tools help you focus on the creative process of
DVD production without having to understand the hierarchy.
A typical DVD hierarchy may look like this: volume>zone>space>domain>video title
set>program chain>part of title>program>cell (smallest addressable unit).
There are two interrelated sides to the hierarchy:
•Navigation (or control) data is the logic that determines the order and conditions of the content
playback.
•Presentation (or object) data is made up of the actual video, audio, and still image content,
including menu backgrounds and subpictures.
A typical DVD chapter menu
A typical DVD chapter menu. In this example, The
Bride button is selected. If activated, playback will
jump to The Bride content.
Button highlighting is typically done with a subpicture overlay. In this case, the subpicture overlay highlights the selection by placing a 40% opacity white
oval over the selected button. Shown below are the
components of this menu.
The object data is combined into multiplexed streams called Video Objects (VOB). Video Objects
are stored in logical containers called Video Object Sets (VOBS). Which Video Object is played
back, and when, is determined by a set of instructions referred to as a Program Chain (PGC),
another logical container.
But let’s start at the very top of the DVD hierarchy, and move through the DVD nomenclature,
looking at how the logical and presentation hierarchy is intertwined.
The top level of organization on a DVD disc is called a volume. A single-sided DVD contains
a single volume; a double-sided disc has two volumes—one for each side. The UDF file system
employed by DVD breaks the volume into zones. In this case, there are two zones: a DVD-Video
zone and a DVD-Others zone. All of the video-related content and navigational data—everything that can be played back by a set-top DVD player—is in the DVD-Video zone, while the
DVD-Others zone contains any non-DVD-Video data, such as desktop computer applications
(which is ignored by a set-top DVD player).
Background graphic
Zones are made up of spaces; spaces are groups of domains—spaces and domains are fairly abstract
logical constructs and beyond this overview.
The first part of the DVD-Video zone that you should be aware of is the Video Manager (VMG),
a special type of Video Title Set (VTS). The Video Manager contains any first-play material, such
as an introductory sequence, as well as the main table of contents menu for the entire volume.
This is the top menu that is invoked when the Top button on the remote control is pressed. There
can be only one Video Manager per volume, and only one top menu (although the top menu
can be stored in different languages. The preferences set for the DVD player determines which is
displayed).
Buttons
The Video Manager may be followed by 1-99 other Video Title Sets, which fill most of the DVD.
A Video Title Set is composed of one or more titles (VTTs—Video Titles) and a VTS Menu
(VTSM) area, which contains a number of menus relating to the content in the VTS. Within the
VTSM, one menu is designated the root menu. The root menu for the Video Title Set currently
being played appears when the Menu button on the remote control is pushed.
Many DVDs have only one Video Title Set. But, because all of the video content in a given Video
Title Set must be in the same aspect ratio, a DVD that offers multiple aspect ratios (for example,
standard and widescreen) must have multiple Video Title Sets.
A Title (TT) is the largest unit of presentation data, or content, on a DVD—usually an entire
movie, TV program, or other presentation. If a disc includes four episodes of a TV series, each
episode might be presented as a separate title. A disc that offers a feature film, a theatrical trailer,
and a supplement might be divided into three titles: The Movie, The Trailer, and The Making of.
Subpicture overlay (40% opacity white oval)
A DVD Primer: From DV to DVD
22
Optionally, a title may be broken down into parts of titles (PTTs) and/or programs (PGs), which
may reflect chapters or scenes, and which may be correlated to menus. Titles, parts of titles, and
programs are made up of cells. The cell is the smallest addressable unit of presentation data in
the DVD hierarchy.
WHAT’S ON THE MENU?
Because there are no details in the DVD-Video specification for menu hierarchies, the manner in which
menus are presented to the end-user is up to the DVD
author. A disc may have no menus or hundreds of
menus. There are six basic types of menu:
Top menu
The top menu is called the Video Manager Menu
because it resides within the Video Manager. There is
only one top menu per volume (that is, only one for
each side of a disc). There may be different language
versions of the top menu. The top menu is often
displayed automatically when the disc is first inserted
in the player, but can also be invoked when the Top
button on the controller is pressed (the Top button
may alternatively be labeled Title, Guide, or Info). The
top menu is sometimes called the title menu, but that
can be misleading if there are multiple titles within
the volume, each title with its own menu.
Root menu
A Video Title Set (VTS) can have a root menu area,
technically called a Video Title Set Menu. Pressing
the Menu button on the controller displays the menu
that has been designated as the root for the currently
active title (often a chapter menu).
A video DVD is more than just movies and menus. A navigation system is necessary for the
viewer to get to the content.
Don’t try to equate a cell with a frame or even with a certain number of frames. A cell may be
as small as an MPEG group of pictures (GOP)—that is, no more than 18 frames for NTSC, 15
frames for PAL and a fraction of a second—or as large as an entire movie.
The presentation data referenced by a title may include a single cell or multiple cells; it may
be made up of cells organized into programs or directly into parts of titles, or it may be made
up of cells that are organized into programs that are further organized into parts of titles. The
breakdown is relevant only to the level of menu navigation that can be implemented. In any case,
the presentation (or object) data is contained in logical units called Video Object Sets (VOBSs).
A Video Object Set is made up of one or more Video Objects. A Video Object (VOB) includes
presentation data—video, audio, subpictures, and navigation data—that is multiplexed into a
stream. Because the data is multiplexed, it can be separated into its constituent parts and called
upon as needed.
The VOB can be considered the basic presentation-data building block of DVD-Video, while the
Program Chain (PGC) is the fundamental logical unit. Each PGC is a set of instructions telling
the DVD player which VOBs should be referenced, under which conditions, and in what order. A
DVD-Video title can, simply, be seen as a collection of PGC (instructions) and the Video Objects
(assets) to which they refer. Different PGCs can reference the same VOBs, selecting different sets
of cells and audio streams to create variations of the content (such as, versions with different
ratings) . Each PGC is made up of a pre-command, a list of content residing in associated VOBs,
and a post-command. The pre-command contains the instructions for playing the content. It is
followed by the list of which VOB content will be played—much like an Edit Decision List (EDL)
in a nonlinear editing system. The post-command contains instructions for what to do after the
list of content has been played—usually to link to another PGC or jump to a menu.
Submenus
The other four kinds of menus are submenus of
root menus, residing in the same Video Title Set.
Many players do not provide buttons for displaying
these submenus, and those that do rely on the DVD
developer to have programmed the appropriate
interactivity. Some players provide a Return, Back, or
Go Up button that may, if the menus are programmed
to take advantage of it, jump back to the parent root
menu. Note that submenus can have submenus of
their own. The names of the four submenu types are
self-explanatory:
•Chapter menu (part-of-title or PTT menu): Button
activation results in a jump to specified PTT (chapter)
or PG (program group or scene) marker.
•Audio menu: Lets viewer select an audio stream
(such as type of audio, language option, or narration
option).
•Angle menu: Lets viewer select a camera angle or
other alternate video stream.
•Subpicture menu: Usually lets viewer select a
subtitle option.
A DVD Primer: From DV to DVD
23
Postcommand
Pre-command
Cell
marker
PTT
t
Video
understanding video and DVD hierarchies
You’re already familiar with the nomenclature of the
video hierarchy—from largest to smallest unit: movie
> chapter > scene > clip > frame > pixel. The DVD
content hierarchy may sometimes seem to parallel
the video hierarchy, but there isn’t always a direct
correspondence. In some hierarchical structures,
there are clear, consistent size relationships between
units. But in video and DVD, the unit relationships are
not defined by size or quantity; a clip can be made up
of any number of frames. Some of the larger units in
the DVD content hierarchy have a capacity limit for
smaller units (for example, a disc can have no more
than 99 titles), but unit boundaries can typically be
defined by the video editor or DVD author.
Cell
Cell
marker
PG
t
Cell
Cell
PTT
t
Cell
Cell
Audio
The anatomy of a Program Chain (PGC)
Region Coding
The motion picture industry has a powerful voice in the DVD Forum, and that’s why the controversial Region Coding feature, also known as country coding, zone lock, and, in computer
drives, Regional Playback Control (RPC), was included in DVD technology. DVDs that contain
Region Coding will only play on devices coded for that region. For example, if you purchase a
DVD player in Canada, it will not play back most prerecorded DVDs purchased outside Region 1.
The code takes up one byte on the DVD. It is designed to search for a matching bit of code in the
DVD player’s firmware. If the proper code is not found, the DVD will simply not play. However,
a disc without a Region Code—also known as an all-region disc—will play on any compatible
DVD player or drive. And there are multiregion players available. In fact, NASA has purchased
and used them on multinational space shuttle flights. But some DVDs from major motion picture studios use a system known as RCE (Region Coding Enhancement), and are unplayable in
multiregion players.
V ide o
Co ntent
H ie r a r ch y
Co mpa r a b le
DV D Co ntent
H ie r a r ch y
M a x im u m
Movie, Project,
or Program
Title (TT)
99 per disc
Chapter
Part of Title (PTT)
or Program Chain
(PG C)
999 per title
Scene
Video Object Set
(VOBS) or Program
(PG)
99 per PGC
Clip
Cell
N/A
A comparison of video content hierarchy and DVD
content hierarchy
Region Coding is not a requirement
The producer of a DVD—whether a major motion picture studio or you—is not required to include
Region Coding. Why would it possibly be a desirable feature? Because movies aren’t always
released everywhere in the world simultaneously and movie studios want to control the timing
of DVD releases in different geographic markets. Region coding also makes it possible to sell
exclusive rights for DVDs to different foreign distributors in discrete geographic markets.
the DVD regions
1. U.S.A., U.S. Territories, Canada
2. Japan, Europe, South Africa, and
Middle East (including Egypt)
5
2
1
2
6
3. Southeast Asia and East Asia (including
Hong Kong)
3
5
4. Australia, New Zealand, Pacific Islands,
Central America, Mexico, South
America, and the Caribbean
4
4
5. Eastern Europe (former Soviet Union),
Indian subcontinent, Mongolia,
Africa, and North Korea
2
6. China
7. Reserved
8
8. Special international venues
(airplanes, cruise ships, and
elsewhere)
A DVD Primer: From DV to DVD
24
The practice of Region Coding is quite controversial. Those opposed to Region Coding suggest
that it may be a violation of fair trade practices. In a court case, the Australian Competition
and Consumer Commission (ACCC) argued that the practical effect of Region Coding is that
consumers who purchase DVD players in Australia are prevented from playing films procured
overseas and, because overseas markets give Australian consumers access to a wider range of
film titles with special features not available locally, the practice amounts to the creation and
maintenance of artificial barriers to trade.
Can DVD Players be modified to permit multiregion playback?
Yes. Special command sequences from the remote control allow some players to switch regions
or play all regions. Some players can be physically modified to play all regions; however this
practice will sometimes void the warranty and may be prohibited by law in some jurisdictions.
Content Protection
Content Protection, like Region Coding, is not a requirement, but is an optional feature of DVD
production. It’s not very difficult to understand why content developers and copyright holders
want Content Protection. So who doesn’t want it, and why? The opponents of Content Protection
claim that its ramifications violate our rights to benefit from open technology and to freely
distribute and share information. There are complex issues involved in the Content Protection
debate—issues involving not only content rights, but also the capabilities (or potential lack of
them) built into the DVD recording technology available to the general public.
CPS and CPSA
Content Protection System (CPS) is the generic term for a technology designed to protect content
from being misused or misappropriated—that is, altered, copied, or displayed in any unauthorized manner.
Content Protection System Architecture (CPSA) is an overall framework for DVD technology
related to controlling access to content recorded on DVDs. Made up primarily of watermarking
and encryption technologies and policies, CPSA includes protection measures for both digital
and analog outputs. CPSA was developed jointly by IBM, Intel, Matsushita, and Toshiba, forming
an alliance known as the 4C Group. The group works in cooperation with the Content Protection
Technical Working Group (CPTWG), a somewhat broader consortium of consumer electronics and
computer companies, as well as content producers. CPSA was designed to encompass the major
Content Protection technologies currently in use, to accommodate the integration of emergent
technologies, and to ensure consistency with and avoid duplication of Content Protection technologies being developed by the Secure Digital Music Initiative (SDMI).
CMI and CCI
Content Management Information (CMI) is the specific logic, or set of rules, governing protected
content. Region Coding is one form of CMI. Simply stated, CMI is just digital code, recorded with
the content and other data on a DVD that may modify the behavior of the DVD device in which it is
played, and may restrict copying of content from protected discs. CMI often modifies playback or
restricts recording attempts regardless of whether the attempt is made by digital or analog means.
Copy Control Information (CCI) is the logic governing if and how content may be copied. CCI is
usually part of the CMI.
Watermarking and encryption
Digital watermarking has been in use for some years in efforts to protect still images from being
used or altered without permission. Watermarking of still images is often quite obvious. Generally, an image watermark is a logo or text that partially obscures the image, and clearly identifies
it as protected. Conversely, for video and audio content, watermarking refers to technologies that
embed CMI in content, so that it is imperceptible to the audience. And unlike the watermarking used to protect still images, video and audio watermarking does not protect the content. The
watermark simply triggers the playback device to respond in accordance with the CMI, so long
as that playback device is compliant with the system being employed. A noncompliant device
will generally not play back watermarked content. The watermark triggers the device to decrypt
encrypted content in accordance with the CMI. Watermarking and encryption/decryption
technology systems are typically made available to content producers and device manufacturers
under license. The license contract specifies the CMI protocols. Watermarking technologies are
standardized by an organization called the Watermarking Review Panel (WaRP).
A DVD Primer: From DV to DVD
25
APS, CPS, copyguard, and Macrovision
An Analog Protection System (APS), also known as an analog CPS (Content Protection System),
prevents analog copies from being made from DVDs. The most widely used APS was developed
by a company called Macrovision and is generally referred to by its trade name. A Macrovision
circuit is built into just about every DVD player, as well as into computer video cards with S-video
outputs. Macrovision-protected discs include trigger bits, encoded in the recorded data that
trigger the Macrovision circuit in the player or video card to send out AGC (Automatic Gain
Control) pulses to the video outputs. AGC pulses interrupt the vertical interval in the television display. The pulses usually do not affect playback on standard TVs, but do affect the AGC
circuitry in VCRs, which results in noise, interference, or other undesirable artifacts on analog
videotape copies.
Adobe Encore DVD supports Macrovision, CGMS,
and CSS Content Protection formats.
Macrovision also uses an additional protection scheme called Colorstripe, which adds a rapidly
modulated colorburst signal that results in lines or stripes appearing across the picture when
analog videotape copies of protected material are viewed. Because the DVD producer pays
Macrovision royalties (typically several cents per disc produced) based on how much protection
is incorporated into the content, and because Macrovision protection can be applied selectively,
not all the content on a Macrovision-protected disc may actually be protected. Both of the
Macrovision techniques—AGC Pulsing and Colorstripe—hinge on interrupting the analog video
signal, so Macrovision can be used to protect only video, not audio, content. There are some
inexpensive devices available that defeat Macrovision, but only a few can be used to circumvent
the Colorstripe scheme.
CGMS and SCMS
Copy Guard Management System (CGMS) is a Serial Copy Management System (SCMS). The
CGMS code embedded in the outgoing video signal is based on one of three rules: copy freely,
copy never, or copy once. The copy once rule allows a first-generation copy to be made, but disallows copies of copies.
CSS
Content Scrambling System (CSS) is a Content Protection solution developed primarily by
Matsushita and Toshiba. It was designed to prevent the direct digital copying of video files from
DVDs, which could result in virtually perfect clones. To play a protected disc, a pair of so-called
keys must match to authenticate both the disc and the device as duly licensed, before allowing an
encrypted MPEG-2 file to be descrambled and played back.
Here’s how it works: approximately 400 master keys are stored in the lead-in area on every
CSS-encrypted DVD. Each licensed hardware (device) manufacturer is given what amounts to
a keyhole (in the form of computer code), matching one of the 400 master keys. This key code is
included in the device’s firmware.
There is no charge for a CSS license, but it is difficult to obtain one, and the license is extremely
restrictive, requiring among other covenants, that Region Coding be employed. If the hardware
license is revoked, the matching key is simply not included on any future CSS-encrypted DVDs.
In order to play a CSS-encrypted disc, the device must include a licensed CSS decryption module
with a valid key code.
When a CSS-encrypted DVD is played in a CSS-enabled device, the plot thickens. In addition to
decrypting the scrambled MPEG-2 file to actually play the video, the CSS decryption algorithm
exchanges keys with the device to generate an incremental encryption code that prevents the further exchange of disc keys and device keys that would be needed to decrypt data from the disc.
The CSS algorithm and keys were intended to be a closely kept secret. However, these days
you can learn every secret on the Internet. DeCSS is a hack that was posted on the Internet in
October 1999, cracking the CSS algorithm and spawning a tangle of legal controversies. The
original version of DeCSS enabled the playback of CSS-encrypted DVDs on computers running the Linux operating system (which had been excluded from CSS because of its open source
approach) and another version works with the Microsoft® Windows operating system. To learn
more about the DeCSS polemic, see www.opendvd.org.
A DVD Primer: From DV to DVD
26
CPRM and CPPM
Content Protection for Recordable Media (CPRM) has stirred up a lot of controversy because it
is a technique that can be applied to a spectrum of storage media, including personal computer
hard drives, where issues related to data recovery and privacy have been cause for concern. As it
relates to DVD, CPRM involves a unique code, physically etched into the burst cutting area (BCA)
of every blank disc. When the disc is played, a CPRM-enabled playback device reads the code from
the BCA and uses it to generate a key to decrypt the content for playback. But if the encrypted
digital content is copied to other media, it can’t be decrypted because the code that generates the
key will be missing or different. Every DVD recorder shipped after 1999 supports CPRM.
Content Protection for Prerecorded Media (CPPM) is designed specifically for DVD-Audio content.
It is based on CSS, but uses a different algorithm developed after the appearance of DeCSS.
DCPS, DTCP, and HDCP
Devised specifically for the next generation of digital TVs and VCRs, DCPS, DTCP, and HDCP
include clandestine key exchanges and encryption/decryption schemes.
The burst cutting area (BCA) near the hub of a
DVD can contain a barcode that provides CPRM
Content Protection.
Digital Copy Protection Systems (DCPS) enable the exchange of data between digital components via lossless, digital connections such as IEEE 1394 (also known as, Firewire, or i.Link),
without permitting perfect digital copies to be created. Several proposals submitted to the Consumer Electronics Association (CEA) from various consumer electronics players call for devices
enabled by digital keys or physical smart cards for renewable security. Such devices exchange
keys and authentication certificates to establish a secure channel whereby other connected but
unauthenticated devices cannot access the signal.
The DVD player itself encrypts the video signal as it sends it to the receiving device, which must
decrypt it. Unauthenticated devices cannot decrypt the signal. All the proposed techniques flag
content with CGMS-style copy freely, copy never, or copy once coding. Players that can authenticate that they are playback-only devices may access all protected content. Recorders can only
receive data flagged as copyable and, as a copy is made, must change the flag to no more copies if
the source is marked copy once.
High-bandwidth Digital Content Protection (HDCP), developed by Intel, is specifically for use
with components connected with digital video monitor interfaces such as the Digital Video
Interface (DVI), designed to replace the analog VGA standard. Most HDTVs are compatible
with DVI. Like DCPS, HDCP uses a complex set of coded keys for device authentication. Upon
authentication, the HDCP protocol encrypts each pixel as it is transferred across DVI from the
DVD player to the digital display. Any unauthorized device that attempts to play back HDCPprotected content transfers only random noise to the display.
How do I make DVDs?
Because this primer isn’t a how-to, you won’t find step-by-step instructions. What you will find
are basics to familiarize you with the tools and process. There are two principal stages to making
DVDs: authoring and replication. For DVD-Video, authoring includes planning, designing,
assembling, and formatting content. Depending upon the software used and individual interpretation, authoring may also include encoding or transcoding video and audio, as well as developing menus.
When authoring is complete, the DVD is replicated. In the professional production environment,
the replication process consists of more than simply burning discs; it also includes premastering,
proofing, quality assurance (QA), physical formatting (during which Content Protection and
Region Coding may be incorporated), and glass mastering.
What tools do I need?
Much of the hardware and software you need is the same as for producing any other video-based
production: tools to create, capture, and edit video. In addition, you’ll need DVD-authoring
software, as well as a device for recording the final content you’ve prepared in the DVD-Video
format, either directly onto DVDs for playback or replication, or onto the half-inch digital linear
tape (DLT) typically used in preparation for mass reproduction. (Most replicators also accept
single-layer DVD-R for replication, but not when copy protection is to be included.)
A DVD Primer: From DV to DVD
27
Hardware
The speed, power, and capacity of many desktop and even laptop systems, make it possible to
go from DV to DVD with a fairly minimal hardware investment, either by using the system
you already own, or by enhancing it somewhat. Answers to the following questions can help you
make your hardware decisions:
•What kind of video will you be incorporating into your productions?
Simple, straightforward editing of DV takes less processing power (that is, MHz) and less random
access memory (RAM) than if you’ll be applying complex visual effects or compositing uncompressed footage. Check the system requirements on your video editing software for guidelines.
But because these system requirements are usually established using a clean computer, you’re
likely to want more than what is recommended. While you may be able to struggle along with
256MB of RAM, you’ll probably be happier with at least 512MB. Many professionals opt for 2GB
of RAM.
•How much video will you be working with?
Digitized video requires significant storage. Uncompressed, a single video frame is approximately 1MB and, therefore, at the NTSC frame-rate of 29.97 fps, 1.5GB is required for just one
minute of video. An hour-long program can consume 90GB of disk space, without even considering all the raw footage that went into it, often five times the amount of the actual product
(450GB), or, for high-end productions as much as 20-50 times (1,800-4,500GB).
To figure the amount of storage you need for DV video (compressed 5:1), allow approximately
216MB for each minute of stored video. Or, looking at it from the opposite direction, each 1GB
of storage holds about 4 minutes and 45 seconds of video. For an hour of DV, therefore, you
would need a 13GB disk.
Let’s say that you’re an event videographer planning on creating DVDs for your clients. To figure
out how much storage you would need to make a two-hour DVD, here’s how you might do the math:
Start with what you need for your finished production—two hours of DV footage
26.0GB
Add a conservative amount for unused footage—at least twice the finished amount
52.0GB
Figure in some additional graphics—titles, for example—and audio tracks
2.0GB
You’ll need space for the MPEG-2 files you export for your DVD
4.1GB
Minimum storage space needed
84.7GB
Example estimate of storage needed for a two-hour DVD
As you can see, you’ll probably need offline storage, such as a large-capacity external hard drive
or two at the very least, or a RAID array or storage area network (SAN) if you’re running a professional operation.
When you consider an offline storage subsystem, capacity isn’t the only factor—transfer rate is
important, as well. To preview video in real time, the data for each frame must be transferred to
and from the processor at the video frame rate—29.97 frames per second for NTSC. The transfer
rate for DV is typically 3.6MB per second. If you are compositing multiple video streams in real
time, that rate must be multiplied for every stream processed concurrently. And the video must
move at a steady, sustained pace, too. If the transfer rate falls below what’s required, frames may
be dropped, resulting in poor quality video. Because faster disk subsystems typically cost more,
you’ll want to configure your system with disks and interfaces that are fast enough to not drop
frames, but not so fast that you’re paying a premium for speed you don’t need.
DVD-RW Drive
TV Monitor
External HD
eo
V id
DVD-Video Player
Audio
IEEE 1394
DV Camcorder
Computer
Entry-level DVD-Video hardware configuration
Amplifier to Speakers
A DVD Primer: From DV to DVD
28
DVD-Video Player
Analog Video Source(s)
Digital Video Source(s)
Vid
eo
Video
Monitor
Video
Monitor
Amplifier to Speakers
Testing
IEEE 1394
Audio Source(s)
io
Aud
MPEG-Encoding
Workstation
Ultra SCSI
External Storage
High-Speed
Network
DVD-Video Authoring
Workstation
Replication
DVD-R Drive
DLT Drive
Graphics
Workstation
Mid-range DVD-Video hardware configuration
•How will you distribute your finished video?
If you need only to burn a small number of final DVDs for personal use, a consumer DVD
writer is all you need. If you have broader distribution plans, you may also need a DLT drive
for recording to DLT, the medium often preferred by DVD-replication facilities, although these
days most replicators will work from a recordable DVD.
Software
Adobe Production Studio delivers the leading-edge software you need to produce professionalquality results for film, video, and DVD. This comprehensive video production toolset is well
integrated, streamlining your workflow to give you more time to be creative and to maximize your
productivity. Adobe applications have similar interfaces, so if you’re familiar with one, you’ll be
able to get up to speed quickly on the others. You can even customize the interface of each Adobe
application to suit your workflow needs and increase your productivity.
If you are upgrading any of your Adobe
video products, make sure to ask about
upgrading to the complete collection.
The Adobe Production Studio is an
incredible value.
Real-time editing for professional video production: When preparing digital video for distribution, you’ll need nonlinear editing (NLE) software such as Adobe Premiere Pro. This revolutionary editing application delivers a host of real-time video and audio editing tools, an elegantly
redesigned user interface, and flexible import and export options.
The essential tool for motion graphics and visual effects: After Effects is the industry standard for
motion graphics and visual effects. Core 2D and 3D compositing tools and effects help you create
eye-catching motion graphics. Sophisticated visual effects tools deliver the precision you need
to produce award-winning output. Easy to learn and use, After Effects pairs a flexible workflow
with exceptional creative options so you can produce professional output for any media, from
film and video to DVD and the web.
A DVD Primer: From DV to DVD
29
The essential tool for professional digital audio: Adobe Audition® turns your computer into a
professional multi-track recording studio with the tools to produce high-quality audio. DVDVideo can deliver unprecedented audio quality when the audio assets you incorporate into your
DVD production are high-quality to begin with.
The world-standard image editing solution: You’ll also need software for creating menu graphics:
Adobe Photoshop is the industry standard for developing still graphics, including backgrounds
and subpictures for DVD menus.
Creative authoring for professional DVD production: Adobe Encore DVD software gives professional
videographers, DVD authors, and independent producers the power to create sophisticated,
multi-language DVDs with interactive menus, multiple audio tracks, and subtitle tracks.
Adobe Encore DVD provides a comprehensive set of tools for designing professional DVD titles.
Unparalleled integration with Adobe Premiere Pro, After Effects, and Photoshop optimizes your
efficiency. Use the convenient Edit Original command in Adobe Encore DVD to open and adjust
your original files in their native applications.
The default Adobe Encore DVD workspace includes panel groups for viewing and working with project settings
and content, and modifying text and graphics, as well as a timeline for laying out content.
Adobe Encore DVD includes a variety of predesigned button and menu styles that are easy to customize to create your own look.
A DVD Primer: From DV to DVD
30
The DVD workflow
No matter how simple or ambitious your project, the DVD workflow can basically be broken
down into seven stages:
1. Planning
2. Asset preparation
3. Authoring
BALANCING YOUR BIT BUDGET
In planning a bit budget, the objective is to balance
the amount of content you include versus its quality.
Start by making a list. In addition to your video assets
(including multiple angles), list all audio streams
including multiple languages and audio formats, as
well as your graphic assets (such as menus, stills, and
subpictures).
Consider both asset size and data rate. The combined
data rates of concurrent streams cannot exceed the
maximum DVD-Video data rate of 10.08 Mbps.
4. Formatting and layout
The data rate (in megabits per second) for each asset
multiplied by the playing time (in seconds) yields the
asset size (in megabits). Asset sizes, when summed,
must fit within the selected disc capacity:
5. Emulation
6. Replication
7. Packaging and delivery
C apacit y in
b illi o ns
of
b y tes
There can be as many variations to this process as there are DVD authors, and the steps that
make up these stages may overlap or may be performed in different stages.
Planning
In the planning stage, you define your project, determining what content to include and how
much and what kinds of interactivity to offer. If you are producing a commercial DVD, you’ll
develop a schedule and milestones, and prepare or confirm a budget. If you are working with
others, you’ll define roles and responsibilities.
If there will be a significant amount of interactivity, you should create a project flowchart, which
can be used as a blueprint for building the DVD.
Audio
Copyright notice
Angles
Studio splash
Subtitles
Title splash
The Making of...
Standard version
Main (Top) menu
Featured movie
Director’s cut
Cast and crew
bios
Audio
Angles
Example of a DVD project flowchart
C apacit y
in M b
( me g a b its)
L ess
4%
o ve r head
in M b
( me g a b its)
A d j u sted
capacit y in M b
( me g a b its)
DVD-5
4.70
37,600
1,504
36,096
DVD-9
8.54
68,320
2,733
65,587
DVD-1O
9.40
75,200
3,008
72,192
DVD-14
13.24
105,920
4,237
101,683
DVD-18
17.08
136,640
5,466
131,174
A spreadsheet with built-in bit budget-balancing
formulas is invaluable. Start by plugging in a desired
level of quality. If the spreadsheet shows you have
too much data to fit on your disc, you can choose to:
a) reduce the amount of content, b) reduce the data
rate of all or some of the assets, or c) move up to a
disc with greater capacity. Option b—reducing the
data rate—reduces the quality of the video when you
encode it.
Some DVD-authoring applications include automatic
bit-budgeting tools that perform the calculations
when you arrive at the formatting (layout) stage. But if
you wait until that point, you may have to go back and
reencode your video to make it fit. Rather than doing
work twice, it makes more sense to budget your bits
during the planning stage of the process. Then, use
the built-in calculator in your authoring application as
a failsafe measure.
Subtitles
You may also develop storyboards that previsualize the production, primarily showing rough
menu layouts and chapter points. Storyboards also serve as important tools for sharing ideas
and concepts.
Bit budgeting is a critical step in the planning stage that ensures all of your content will fit on the
DVD. It’s good practice to reserve some space for changes or additions as the process unfolds.
Because of the possibilities inherent in DVD, it’s easy to get carried away, shooting multiple
angles and creating branching options or alternate endings. Don’t forget that for every additional
camera angle you want to include on your DVD, you increase the bits you need to budget for the
scene by 100 percent.
A DVD Primer: From DV to DVD
31
Preparation
Preparation means gathering and preparing all of the assets that will be included on your
DVD—video, audio, and graphics.
The quality of your DVD is largely dependent upon the quality of your source material. Do your
best to make sure that you gather the highest quality versions available for all of your assets.
For existing video, digital tape is generally better than analog, assuming that the original source
was digital. If your content was originally shot as analog footage, you want the closest you can
get to first generation because, with every generation copied, analog loses fidelity. If you do use
videotape, test tones and color bars are valuable tools for calibrating your playback deck to match
the recording deck.
If your footage was shot in 24P mode, keep your entire workflow in progressive mode for easier
editing and encoding.
Video assets generated on the computer, such as motion graphics and visual effects, should be
provided digitally, rather than on tape (either digital or analog)—preferably uncompressed, as
AVI, MOV, or OMF files.
If you are shooting footage for your DVD, preparation includes preproduction, production, and
post-production stages—planning, shooting, capturing, editing, and adding effects, as well as
encoding.
After your video has been collected and edited, you may want to preprocess it using filters or
Digital Video Noise Reduction (DVNR) processors designed to minimize any undesirable
video artifacts resulting from MPEG encoding. DVNRs are available in a variety of different
forms ranging from hardware to software plug-ins.
Your audio must also be recorded or collected, sweetened as necessary before encoding, and
synchronized with your video. For audio assets, the higher the sample rate and the bit depth, the
better your end product will be. The more information you start with, the better your results will
be when you downsample and encode. Adobe Audition offers a wide variety of powerful options
for sweetening and cleaning up your audio.
You then must create menu backgrounds and subpictures. Original menu design requires excellent graphic design skills and a thorough understanding of the limitations, so consider using a
DVD authoring application such as Adobe Encore DVD, which comes with customizable menus.
Once your video and audio assets have been collected, edited, and preprocessed, they must be
encoded for DVD: video as MPEG-2 and audio in one of the audio formats specified for DVDVideo. Encoding can be handled in Adobe Premiere Pro or right within Adobe Encore DVD.
Authoring
If your DVD-authoring software includes MPEG-encoding capabilities, you might save encoding
for this stage, as long as you are willing to give up some of the fine control you have over the
encoding process with more sophisticated encoding solutions. Similarly, if your authoring software provides menu templates, you may create (that is, customize) your menu graphics as part of
the authoring stage, as well. Typically, however, the authoring stage involves five steps:
1. Identifying the media assets to be incorporated in the DVD project. The actual asset files are
not really copied or moved anywhere in this step. Rather, their locations on the system are
identified and links to those locations are generated.
2.Assembling the video and audio assets, identifying chapter points, titles, and title sets. Most
DVD-authoring applications use timelines with drag-and-drop functionality to make this
step and the next one easier.
3. Organizing the presentation groups to match the project flowchart.
A DVD Primer: From DV to DVD
32
4.Programming functionality and interactivity. Define the links between the various presentation groups, along with what should happen when the viewer presses the various buttons on
the player remote control. Create menus by importing background graphics and subpictures
into the authoring application. Then, link menu buttons to content assets and other menus.
5. Simulating the final product by testing menus and navigation. Your DVD-authoring software
should let you see how your DVD will look and perform in a player. Some authoring systems
will warn you of potential problems in some players. But this is only the first of several QA
steps in the overall process.
Formatting and layout
After you’ve completed the steps of the authoring process, the various video, audio, and still
picture streams must be multiplexed, or muxed. Then, the content and its associated navigation
(or control) information must be formatted as special types of data files that are compliant with
the DVD-Video specification: VOBs (video object files), BUPs (backup files), and IFOs (the information files that tell the player how to access the data stored in the VOBs).
Once formatting is finished, the DVD-authoring software performs the layout process, resulting
in a volume image (also known as disc image).
Formatting and layout take time. The amount of time depends on the processing speed and power
of the computer, the type of authoring software, and the size and complexity of your DVD content. Most DVD authoring tools can perform formatting and layout in real time, meaning that if
the actual playing time of your DVD content is two hours, then real-time formatting and layout
take two hours. Some DVD authoring tools can also write directly to the DVD at the same time.
Emulation
Simulation tests the functionality of components of the DVD, or the DVD project as a whole,
from within the DVD authoring application. Emulation, on the other hand, tests the DVD
project outside the authoring tool. Most DVD authors burn a DVD-R for emulation, and then
test it on as many different hardware players as possible. Emulation may catch problems that go
unnoticed in the simulations run during the authoring stage. During emulation, you can test the
DVD to make sure that:
•First-play material plays first.
•Video and audio are of the anticipated quality.
•Video and audio are synchronized.
•Menus look and operate as intended.
•Subpictures (that is, subtitles) appear when they are meant to and are clearly readable.
•Closed captions can be decoded by a TV set.
•Parental controls function, and user operations (that is, the functionality of player controls)
behave as expected.
Dual-layer DVD burners are now available, which can be a real lifesaver for testing projects that
won’t fit on a single layer. If you don’t have access to a dual-layer DVD burner, you can use software emulation to play the material from the disc image rather than from a DVD.
Mass DVD replication requires a number of
specialized, precision machines to automate
multiple processes, while maintaining quality.
Replication
If you are creating just a few final DVDs, the replication stage involves just burning the required
number of discs onto DVD-R using a DVD writer. However, if you will be replicating something
on the order of a thousand or more DVDs, there are a few more steps:
•lf you will be implementing Content Protection or Region Coding, you’ll need to f lag these
options using your authoring tool, and create a new disc image. The actual encryption is done
in the final replication stage, as the replicator will hold the licenses and keys for these processes.
(Note that not all DVD authoring applications allow this functionality.)
A DVD Primer: From DV to DVD
33
•Premastering is the process of writing your final disc image to the digital linear tape (DLT) or
DVD-R that will be sent to the replicator. DLT is generally preferred and must be used if Content Protection or Region Coding are to be employed.
•Physical formatting converts the disc image provided on the DLT or DVD-R into the bitstream
needed by the laser beam recorder (LBR). Among other processes, the data is encrypted for
Content Protection and Region Coding, interleaved, and error correction added during physical
formatting.
•Glass mastering is the process of creating a model of the final DVD, which is used for generating
stampers. A stamper has the inverse of the pits and tracks on the glass master. Stampers wear
out fairly quickly during the fabrication process, so multiple stampers may be produced from
the glass master to complete the run.
•Molding, sputtering, bonding, and labeling complete the replication process. Plastic copies of
the glass master are made from the stamper, using an injection-molding process. A thin metallic
layer is sprayed onto the polycarbonate (plastic) substrate. The two sides of the disc are then
bonded together—DVD-5 discs and some DVD-9 discs get bonded to a blank side, while twosided discs are bonded back to back. For one-sided discs, most of the surface of the back side
is available for labeling, in designs that range from one color to full-color. For two-sided discs,
the print area is limited to within the burst-cutting area. Depending on the type of disc and the
printing method selected, the disc may be labeled before or after bonding.
•Check discs are a limited run of proof discs created by the replicator. They should be run
through the same rigorous testing process as was performed in the emulation stage. This is the
DVD author’s last opportunity for QA before discs are mass produced. Once check discs have
been approved, it is the replicator’s responsibility to make sure the final fabricated discs match
the check discs.
Packaging and distribution
DVDs, once fabricated, are inserted into packages with any printed material that may be designed
to house or accompany them. Commercial printers and packaging specialists can help the designer with keylines or templates to use as guides for packaging graphics. Illustrator, Photoshop,
and Adobe InDesign® software are often used to develop the artwork for packaging and inserts.
Once packaged, DVDs are shrink-wrapped, boxed, and shipped.
Resources
HOW TO PURCHASE ADOBE SOFTWARE PRODUCTS
Via web:
www.adobe.com/store
Via phone:
Call the Adobe Digital Video and Audio Hotline at: (888) 724-4507
Education customers:
Find an Adobe Authorized Education Reseller at:
www.adobe.com/store/general/otherplaces/uscanada/educlist.jhtml
To find the reseller nearest you, visit:
www.adobe.com/store/customerregistration/other_places.jhtml
A DVD Primer: From DV to DVD
34
Glossary
Academy Aperture: Standard 4:3 aspect ratio, so called because it was adopted by the Academy of
Motion Picture Arts & Sciences (in 1927) as the industry standard.
AC-3: Often used in reference to DVD because this is how the technology is referred to in the
DVD standards documents.
Analog: Refers to video and audio recorded or stored nondigitally. Older video formats such as
VHS and Hi 8 are analog.
Anamorphic: Refers to an image or to the technique used to create images where the visual information in a widescreen view is horizontally squeezed into the narrower proportion of a standard
4:3 image. For proper viewing, the image is expanded back to its original wide format.
Angle: Also known as a camera angle, a scene recorded from an alternate viewpoint. When used
in DVD Video, angles offered as alternate video tracks must be of the same duration. Up to nine
angles (total) are allowed by the DVD Video specification.
Angle menu: DVD menu used for the selection of alternate angles.
AOB: Audio Object on a DVD-Audio file.
AOBS: Audio Object Set on a DVD-Audio file.
Artifact: An undesirable distortion of the audio or video, typically a byproduct of an electronic
or digital process. In digital video, artifacts usually result from color compression and are most
noticeable around sharply contrasting color boundaries, such as black next to white.
Aspect ratio: The ratio of an image’s width to its height. For example, a standard video display
has an aspect ratio of 4:3. Pixel aspect ratio refers the shape of a nonsquare pixel.
Assets: The video and audio clips, stills, titles, and any other materials that make up the content
of a video or DVD production.
Audio sweetening: Processing audio to improve sound quality or to achieve a specific effect.
Authoring: For DVD Video, the process of planning, designing, assembling, and formatting
content. The authoring process may, depending upon the software being used and individual
interpretation, include encoding video and audio, as well as creating menus.
Autoplay: Describes content that is programmed to start playback automatically when a DVD is
inserted into a DVD player that supports automatic playback.
Bandwidth: The data-carrying capacity of a device or network. Bandwidth is the maximum
amount of data that can travel a communications path in a given time, usually measured in kilobits per second (Kbps) or megabits per second (Mbps). Connections of 56 Kbps or lower (typical
dial-up connection rates) are considered low bandwidth or narrowband. High bandwidth, or
broadband, connections are higher than 56 Kbps (for example, ISDN, DSL, cable modem, T1).
Binary: A type of digital system used to represent computer code in which numerical places can
be held only by 0 or 1 (off or on).
Bit: The smallest unit of data used by computer systems. A bit (short for binary digit) has a value
of either 0 or 1. Bits are the building blocks of binary data.
Bit depth: For audio, the number of bits used to represent each sample; for video, the number of
bits used to represent each channel of a sample. See Bitmap.
Bitmap: Also known as a raster, bitmap data includes a set of binary values specifying the color
of individual pixels that make up an image. Bitmap data is characterized by resolution and bit
depth. Resolution relates to the detail in an image, and is expressed in dots per inch (dpi) or
pixels per inch (ppi). The higher the resolution (that is, the more dots used to describe the image),
the more detail possible.
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Bit depth defines the number of bits that are used to represent each color channel or bits per
channel (bpc). The higher the bit depth, the more colors can be displayed. A high-contrast (no
grey tones) black and white image is 1 bit. As bit depth increases, more colors become available:
Bit
depth
M a x im u m co lo r s
1
2
2
4
4
16
8
256
16
32,768
24/32
16.7 million
For image detail and quality, bit depth is as important as resolution, because the bit depth determines the available colors. When fewer colors are available, areas that may have shown a subtle
shift of tones and hues are rendered as single blocks of solid color, eliminating image detail.
Bitmap data is indispensable for continuous tone images, such as scanned or digital photographs,
and for antialiased images. However, bitmap data is consistently larger than vector data.
Each pixel in a bitmap image has to be defined. A relatively small 150 x 150-pixel graphic requires 22,500 discrete bits of information plus the palette, or color lookup table (CLUT), which is
usually included.
Blu-ray Disc: Not yet brought to market, but specified by a group of companies that make up the
Blu-ray Disc Association (BDA). This 25GB capacity optical disc technology accommodates high
definition (HD) feature-film length content. Based on a blue violet laser rather than the currently
standard red laser, Blu-ray Disc requires industry retooling and new players for consumers.
Camcorder: A video camera that includes a device for recording audio and video.
Camera angle: See angle.
Capture: If the source footage is analog, capture refers to the act of digitization (conversion to a
digital format) to make the video usable on a computer. When capturing, you may also compress
the video to a manageable data rate for processing and storage. If the source video is DV, capture
typically refers to the simple transfer of video from an external device, such as a digital camcorder
or tape deck, to a computer hard drive.
Capture card: See video capture card.
CBR: Constant bit rate. This type of compression results in a fixed data rate. The amount of compression applied must vary to produce the selected data rate. Complex scenes that require greater
compression to match the selected data rate may result in poor quality. Contrast with VBR.
Chrominance: The color portion of a video signal.
Clip: A digitized portion of video.
Codec: Short for compressor/decompressor or coder/decoder; software or hardware that encodes
data for storage or transmission and decodes the data for playback. Encoding very often includes
compression; decoding often includes decompression.
Color sampling: A method of compression that reduces the amount of color information (chrominance) while maintaining the amount of intensity information (luminance) in images.
Compositing: The process of combining two or more images.
Compression: Reducing the amount of digital data used to represent still image, video, audio, or
other information to yield efficiencies in storage and transmission.
Compression ratio: Degree of reduction of digital data.
Data rate: Amount of data moved over a period of time, such as 10MB per second. Often used to
describe a device’s ability to retrieve and deliver information.
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Digital: Refers to a type of signal that represents values numerically, which allows computers to
manipulate and store them more easily.
Digitizing: Process of converting an analog audio or video signal to digital information.
Dolby Digital: Developed by Dolby Laboratories, Dolby Digital has become the most commonly
used audio coding system for DVD-Video. The DVD-Video specification for NTSC requires at
least one audio track in either Dolby Digital or PCM; DVD-Video for PAL requires at least one
Dolby Digital, PCM, or MPEG 2 audio track. Dolby Digital can have from one to five full-range
channels, plus an LFE (Low Frequency Effects) channel. Full surround sound Dolby Digital,
utilizing all available channels, is often referred to as 5.1 sound. Also see AC-3.
Dolby Pro Logic: Developed by Dolby Laboratories, the decoding process and the circuit used to
apply the process of separating discrete audio surround sound channels from a matrix-encoded
Dolby Surround signal.
DTS: Digital theater systems, originally developed for use in theaters. DTS is an optional audio
format for the DVD-Video specification.
DTV: Digital television.
Duration: The length of time a video or audio clip plays, or the difference in time between a clip’s
In point and Out point.
DV: Generally refers to digital video, but current usage suggests a number of specific definitions:
1) the type of compression used by DV systems, 2) the format that incorporates DV compression,
or 3) a special type of tape cartridge used in DV camcorders and DV tape decks.
DVD: An optical storage medium that looks like a CD but has a much higher storage capacity—more
than enough for a feature-length film that is compressed with MPEG-2. DVDs require special
hardware for playback.
DVD Forum: International consortium of consumer electronics, computer, and entertainment
industry leaders that established the initial standards for DVD technology. The DVD Forum is
also responsible for HD-DVD, the standard for next generation DVDs that can hold full-length
movies in high definition.
DVD Multi: A logo program overseen by the DVD Forum that identifies DVD devices (players
and writers) that support all three DVD formats: DVD-RAM, DVD-R, and DVD-RW.
DVD-RAM: The first rewritable DVD format introduced; a double-sided disc requiring a special
cartridge for handling and recording to avoid damage to the fragile recording surface.
DVD-ROM: A term used to refer to both the physical and application layers of the DVD formats.
DVD-R/DVD+R: Write once recordable DVD formats, often referred to as DVD minus R and
DVD plus R. DVD R(A), or DVD for Authoring, is used by professionals to generate masters
for replication. DVD-R(G), or DVD for General, was developed for the consumer market and
incorporates content protection measures that prevent copying of specially protected entertainment titles.
DVD-RW/DVD+RW: Rewritable DVD formats, often referred to as DVD minus RW and DVD
plus RW.
DVNR: Available as hardware or software plug-ins, Digital Video Noise Reduction processors can
be used to minimize any undesirable video artifacts resulting from MPEG encoding.
DVS: Descriptive Video Services may be included as an alternate audio track on DVD Video,
augmenting the standard soundtrack by describing the action so the program can be enjoyed by
visually impaired audiences.
DV25: The most common form of DV compression, using a fixed data rate of 25 Mbps.
EDL: Edit decision list; a master list of all edit in and out points, plus any transitions, titles, and
effects used in a film or video production. The EDL can be input to an edit controller, which
interprets the list of edits and controls the decks or other gear in the system to re-create the
program from master sources.
A DVD Primer: From DV to DVD
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Effect: A process applied to a frame or frames of video to change its appearance.
Fields: The sets of odd and even lines drawn by the electron gun when illuminating the phosphors on the inside of a standard television screen, which results in the display of an interlaced
image. In the NTSC standard, one complete vertical scan of the picture or field contains 262.5
lines. Two fields make up a complete television frame; the lines of field 1 are vertically interlaced
with field 2 for 525 lines of resolution.
FireWire: Apple Computer trade name for IEEE 1394.
fps: Frames per second; a unit of frame rate.
Frame: A single still image in a sequence of images which, when displayed in rapid succession,
creates the illusion of motion. The more frames per second (fps), the smoother the motion appears.
Frame rate: The number of images (video frames) shown within a specified time period; often
represented as fps (frames per second). A complete NTSC TV image consisting of two fields, a
total scanning of all 525 lines of the raster area, occurs 29.97 times a second. In countries
where PAL and SECAM are the video standard, a frame consists of 625 lines, with a frame
rate of 25 fps.
Fullscreen: Format that uses the entire standard aspect ratio (4:3) television screen by (a) displaying material shot in Academy Aperture, (b) lopping off the ends of widescreen material, or (c)
employing the pan-and-scan technique to select the optimal 4:3 shots from widescreen.
Generation loss: Incremental reduction in image or sound quality as a result of repeated copying
of analog video or audio information and usually caused by noise introduced during transmission.
Generation loss does not occur when copying digital video unless it is repeatedly recompressed.
Headroom: When capturing audio, extra data acquired as a result of capturing at higher quality
settings than needed for the final cut. Headroom helps preserve quality when adjusting audio
gain or applying certain audio effects.
HD: Abbreviation used to refer to high-definition video.
High Definition Television (HDTV): A monitor or display offering 720p (1280 x 720 pixels progressive) or 1080i (1920 x 1080 pixels interlaced) resolution, and capable of displaying a 16:9 image
and supplying high-quality, multichannel surround sound. Also, the technology used to create
and deliver content meeting HDTV standards.
High Definition DVD: The next generation of DVD technology, which will provide enough storage
on a single disc to deliver a feature-length film as high definition (HD) quality video.
IEEE 1394: The interface standard that enables the direct transfer of DV between devices such
as a DV camcorder and a computer. Also used to describe the cables and connectors using this
standard.
i.LINK: The Sony trade name for IEEE 1394.
Interframe compression: Reduces the amount of video information by storing only the differences between a frame and the frames adjacent to it. (Also known as temporal compression).
Interlaced display: System developed for early television and still in use in standard television
displays. The electron gun used to illuminate the phosphors coating the inside of the screen alternately draws even, then odd horizontal lines. Each scanning of the image is called a field. To produce
the approximately 30 frames per second of NTSC TV, the screen shows half the lines composing each
frame (each field) about every 1/60th of a second. We perceive these interlaced fields of lines as
complete pictures. The actual frame rate for NTSC video is 29.97; the field rate is 59.94.
Intraframe compression: Reduces the amount of video information in each frame, on an individual basis. (Also known as spatial compression).
JPEG: File format defined by the Joint Photographic Experts Group of the International Organization for Standardization (ISO) that sets a standard for compressing still computer images. Because
video is a sequence of still computer images played one after another, JPEG compression can be
used to compress video (see MJPEG).
A DVD Primer: From DV to DVD
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Keyframe: A frame selected at the beginning or end of a sequence of frames, that is used as
a reference for any of a variety of functions. For example, in interframe video compression,
keyframes typically store complete information about the image, while the frames inbetween
may store only the differences between two keyframes. Or, in applying an effect to a video clip,
keyframes may contain values for all the controls in the effect and, when the values are different
for the beginning and ending keyframes, the effect changes over time.
Land: The flat areas surrounding pits on the recording surface of an optical disc.
Letterbox: When the full width of a widescreen image is preserved on the screen of a standard
4:3 TV, black bars are placed above and below the image to block out the unused portions of the
screen so the widescreen image can be viewed as originally intended. DVD Video players can
automatically letterbox a widescreen image for viewing on a 4:3 TV.
LFE: The low frequency effects channel in 5.1 channel surround sound such as Dolby Digital or
DTS is used to reproduce low frequency sounds in the 5-120 Hz range (for example an explosion,
the roar of a locomotive or jet engine, or the rumble of a spacecraft). While a subwoofer may be
used for the .1 channel, it can be played back through any speaker that has adequate dynamic
range.
Lossless: A process that does not affect signal fidelity; for example the transfer of DV via an IEEE
1394 connection, or a lossless compression scheme such as RLE.
Lossy: Generally refers to a compression scheme or other process that strives to maintain as
much quality as possible while reducing storage requirement, but does result in some degradation of signal fidelity.
Luminance: Brightness portion of a video signal.
Markers: Markers are used in the editing process to indicate important points in the timeline or
in individual clips. Markers are for reference only; they do not alter the video program.
Matrix encoding: The process of combining multiple audio surround sound channels into a standard dual channel stereo signal. Also referred to as phase matrix encoding.
MPEG/MPEG-1/MPEG-2: The Moving Picture Expert Group of the International Organization for
Standardization (ISO) and International Electrotechnical Commission (IEC) have defined multiple standards for compressing audio and video sequences. MPEG compression uses a technique
where the differences in what has changed between one frame and its predecessors are calculated
and encoded. MPEG is both a type of compression and a video format. MPEG-1 was initially
designed to deliver low data rate video through a standard speed CD, and is typically used for
Video CDs and web video delivery. MPEG-2 provides broadcast quality video, and is most often
used for DVD. MPEG-1 and MPEG-2 require a special decoder for playback.
MPEG audio: Audio compressed according to the perceptual encoding standard specified by the
Moving Pictures Expert Group. MPEG-1 audio provides two channels for stereo playback, which
can be in the Dolby Surround format. MPEG-2 audio offers up to 7.1 channels of audio for a true
surround experience. MPEG audio is mandatory for DVD Video in the PAL format.
MPEG video: Video compressed according to the specifications of the Moving Picture Expert
Group.
NLE: Nonlinear editing.
Noise: Any signal that is added to the original. That is, any distortion of the pure audio or video
signal that would represent the original sounds and images recorded.
Nonlinear editing: Random access editing of video and audio on a computer, allowing for edits
to be processed and reprocessed at any point in the timeline, at any time. Traditional videotape
editors are linear because they require editing video sequentially, from beginning to end.
NTSC: National Television Standards Committee standard for color television transmission used
in the United States, Japan, and elsewhere. NTSC incorporates an interlaced display with 59.94
fields per second, and 29.97 frames per second.
A DVD Primer: From DV to DVD
39
Optical disc: Removable storage medium that is written and read using laser light (for example,
CDs and DVDs).
PAL: Phase-alternating line television standard used in most European and South American
countries. PAL uses an interlaced display with 50 fields per second, or 25 frames per second.
Pan-and-scan: A technique for converting a widescreen image to conform to a different aspect
ratio (usually 4:3 for TV) by reframing the image (that is, cropping out parts of the picture).
DVD Video players can automatically create a 4:3 pan-and-scan version from widescreen video
by using a horizontal offset encoded with the video.
PCM: Pulse code modulation, the uncompressed representation of audio signals in digital form.
PCM is derived by sampling the analog waveform at regular intervals, quantizing the samples,
and generating a series of pulses represented by digital code. PCM is one of the audio formats
that may be used to fulfill the requirements of the DVD-Video specification, but is rarely used in
favor of one of the compressed audio formats, typically Dolby Digital.
Phase matrix encoding: See matrix encoding.
Pitch: The amount of space between tracks on an optical disc.
Pits: Microscopic depressions in the recording layer of an optical disc that are read by a laser
beam in the player and translated into a binary stream, which is then decoded for playback.
Contrast with land, the flat areas surrounding pits.
Pixel: Picture element, the minimum computer display element, represented as a point with a
specified color and intensity level.
Post-production: The phase of a film or video project that involves editing and assembling footage and adding effects, graphics, titles, and sound.
Preproduction: The planning phase of a film or video project usually completed prior to production.
Previsualization: A method of communicating a project concept by creating storyboards, rough
animations, or edits.
Production: The phase of a film or video project including shooting or recording raw footage.
Progressive scanning display: A method for displaying video that shows all the scan lines in one
pass (compare to interlaced display).
Resolution: The amount of information in each frame of video. In digital video, resolution is
represented by the number of horizontal pixels times the number of vertical pixels (for example
720 x 480).
RGB: Red-Green-Blue: a way of defining a color in terms of the amounts of the three primary
colors (in the additive color system) that must be combined to display that color on a computer
monitor.
Sample rate: In digital audio, the number of samples per second.
Scope: Short for Cinemascope, the first commercially successful widescreen format. Scope became
the generic term for film either shot or exhibited in any widescreen format.
SDDS: Short for Sony Dynamic Digital Sound. SDDS is an optional audio format for DVD-Video
originally developed for theater surround sound.
Spatial compression: See intraframe compression.
Subpicture: A bitmap graphic overlay used in DVD-Video to create subtitles, menu highlights,
and more.
Temporal compression: See interframe.
Time code: The time reference added to each video frame that enables accurate editing; may be
thought of as the address where a clip starts (in point) or ends (out point).
Timeline: The graphical representation of program duration, on which video, audio, and graphics
clips are arranged.
A DVD Primer: From DV to DVD
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Track: (1) On the recording surface of an optical disc, a single revolution in the continuous spiral along which the pits are arranged. (2) In reference to DVD content, a discrete
element such as a video, audio, or still image stream. For any given sequence, the DVDVideo specification allows up to nine different simultaneous video tracks, or angles; up
to eight tracks of digital audio; and up to 32 subpicture tracks.
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24-bit color: Type of color representation used by most computers. For each of the red,
green, and blue components, 8 bits of information are stored (24 bits total). With these
24 bits of information, over 16 million different colors can be represented.
Uncompressed: Digitized video that has no information removed from it. Also called
raw video.
VBR: Variable bit rate compression. Strives to glean the most efficient use of available
bandwidth and produce consistent quality by allowing the data rate to vary between
selected minimum and maximum rates. Contrast with CBR.
Video capture card (or board): A hardware component that adds the functionality
needed to digitize analog video. Using a hardware or software codec, the capture card
can also compress video In and decompress video Out for display on a television monitor.
Widescreen: Any aspect ratio for film and video wider than the standard 4:3 format.
Widescreen previously referred to wide-aspect film formats, but is now typically used to
refer to the 16:9 format that has become standard widescreen for DVD (the aspect ratio
specified for HDTV).
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and Mac are trademarks of Apple Computer, lnc.,registered in the
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