DVD has become an
increasingly popular way to store and playback videos.
This disk based video storage has the same advantages
over video tape that an audio CD has over an audio
cassette tape. Video rental stores, once stocked
exclusively with VHS tapes, now have growing DVD
sections. As the price of DVD players comes down the
future of DVD seems bright.
Basic Definitions
DVD is an
optical disk storage technology. It can store high
quality video, high quality audio and computer data. The
DVD is the acronym for Digital Versatile Disk. You may
have heard DVD referred to as Digital Video Disk.
Because the disks can be used to store data as well as
video the more general term is the currently accepted
term.
DVD-Video, often
simply called DVD, defines how video programs are stored
on the DVD disk and played on a DVD-Video player or DVD-ROM
drive in a computer.
When you hear the term
"DVD-ROM" it may refer to either DVD-ROM
drives or DVD-ROM disks. DVD-ROM drives are the DVD disk
drives that can be installed in computers to read DVD
disks. DVD-ROM drives can also read CD-ROMs. DVD-ROM
disks (instead of drives) refer to manufactured DVD-ROM
disks. These are the disks that you buy with the
video/audio/data already recorded on the disk.
(Note: ROM = Read Only
Memory, or a permanently recorded storage medium that
can be read, but can only be recorded to one time,
during manufacture.)
DVD Players are
the specialized stand alone machines that are used to
play DVD disks. So far there have been 3 major
revisions, or 3 generations. Sometimes a disk that
cannot play on an older machine can be played on a 3rd
generation DVD Player.
While CD-ROM disks can
be read by DVD-ROM drives and DVD players, some brands
of CD-R disks (the blank CDs that can be written to by a
CD burner) cannot be read by some DVD Players or
DVD-ROM drives. This is because the dye used by some CD-Rs
may be "invisible" to the DVD laser
wavelength. Some DVD Players have a "dual
laser" or "dual optics" feature to allow
the DVD Player to read CD-R disks.
A DVD disk is
exactly the same physical size as a CD. As well as DVD-ROM
disks DVD disks include several types of disks that can
be recorded (or burned) such as DVD-R, DVD-RAM, DVD-RW
and DVD+RW.
DVD Production
There are 4 major steps
in DVD Production:
1) Encoding the content
to MPEG2 video files and digital audio files
2) Authoring
(navigation design, layout and testing)
3) Premastering
(creating a disk image)
4) Duplication (under
50 copies using DVD-R disks) or Replication (mass
production at a DVD manufacturing plant)
DVD Video Files
– MPEG2
If you want to record
video onto a DVD disk you will have to create MPEG2
files that meet the DVD video requirements. These are
fairly exact requirements.
DVD-Video may have up
to 8 audio tracks (streams). Each track can be in one of
3 formats: Dolby Digital (AC-3), MPEG1 Layer 2 audio (MPA
or MP2), or PCM (WAV). The audio must be sampled at 48
kHz (as opposed to the 44.1 kHz for an audio CD) with a
minimum of 16 bits/sample.
The DVD specifications
(adhered to by DVD Players) requires a maximum bit rate
of 10.08 Mb/s for DVD Video disks. This is the maximum
bit rate for the video, the audio, and the subpicture
stream. The maximum video bit rate is 9.8 Mb/s, but
normally a video bit rate of 6 Mb/s will appear lossless.
For just the video and the audio streams the recommended
maximum bit rate is 9 Mbits/s. For example, if you
encode your video at 6000 Kbits/sec and your audio at
1540 Kbits/sec (an uncompressed WAV file) your combined
bit rate will be 7540 Kbits/sec. If you add more audio
streams (up to a maximum of 8 audio streams) your
combined data rate will be the video data rate plus the
audio bit rates of all of the audio streams (not
just the video and the single audio stream that will be
playing at one time).
DVD Navigation
The most simple type of
DVD Video disk has a single movie (or title). When you
place the DVD disk in the DVD Player the movie starts
playing. Disk playback can be controlled using the usual
transport controls found on the DVD Player's remote
control.
Many DVDs have a menu
to provide the viewer with content selection and feature
control options. Each menu has a background graphic
and/or buttons (or hotspots).
DVD-Video content is
broken into "movies" (sometimes
referred to as titles or, for audio DVDs, albums) and
"starting points in movies" (chapters
or songs). Sometimes the entire DVD is referred to as a
"DVD title".
Movies are
normally created from a single VOB file (video
object file). The VOB file is normally created from an
MPEG1 or MPEG2 file and 1 to 8 audio files. Some DVD
authoring software allows you to use chapters in your
movie for navigation to a specific starting place. You
can then create buttons to take viewers to a specific
chapter point. Note: chapters are starting places only.
You cannot mark the "end of a chapter".
Alternately, with some
DVD authoring tools, movies may be made up of
"cells" linked together by one or more
"program chains" (PGC). A PGC can be on of
three types: sequential play, random play (may repeat),
or shuffle play (random order but no repeats).
Individual cells may be used by more than one PGC, which
is how parental management and seamless branching are
accomplished: different PGCs define different sequences
through mostly the same material.
DVD Remote Controls:
All DVD remote controls have 4 arrow keys to allow the
viewer to select onscreen buttons, plus a select (or
activate) key, numeric keys, a menu key and a return
key. DVD Remote controls may include a variety of other
functions, such as next, previous, search to part of
title (chapter) and select audio track (using one of 8
languages).
DVD versus CD
DVD and CD disks are
physically exactly the same size. However, that is where
the similarity ends. CDs can often be played in DVD
drives, but DVDs cannot be played in CD drives.
DVD drives use a laser
with a smaller wavelength. A DVD laser uses 650 nm or
635 nm wavelength while a CD laser uses a 780 nm
wavelength. A DVD packs the data closer together
(smaller track pitch and shortest pit length). It also
spins faster. A 1x CD-ROM can deliver up to 1.168 Mbits/sec
while a 1x DVD can deliver up to 10.6 Mbits/sec. A CD-R
has a data capacity of 650 Mbytes. A DVD-R has a data
capacity of 4.38 GB. A DVD-ROM disk can hold up to 15.9
GB.
DVD Drive speed
The DVD specifications
(adhered to by DVD Players) requires a maximum bit rate
of 10.08 Mb/s for DVD Video disks. This is the maximum
bit rate for video plus audio plus subpicture. The
maximum video bit rate is 9.8 Mb/s, but normally a video
bit rate of 6 Mb/s will appear lossless.
A 1x DVD-ROM drive
provides a data transfer rate of 1.321 MB/s (or
approximately 11 Mb/s, where 1 Byte = 8 bits). This is
roughly equal to a 9x CD-ROM drive (the 1x CD-ROM data
transfer rate is 150 KB/s or 0.146 MB/s). DVD-ROM drives
are currently available in 2x, 4x, 4.8x, 5x, 6x, 8x,
10x, and 16x speeds.
Note: When playing
movies, a fast DVD-ROM drive gains you nothing more than
possibly smoother scanning and faster searching. Speeds
above 1x do not improve video quality from DVD-Video
discs. Higher speeds only make a difference when reading
computer data, such as when playing a multimedia game or
when using a database.
Recordable DVD
Disks: DVD-R (A), DVD-R (G), DVD-RAM, DVD-RW,
and DVD+RW
There are currently 5
different types of recordable DVD disks. Unfortunately,
none of these formats are fully compatible with each
other or with existing DVD-ROM drives and DVD Players.
DVD-R disks can
record data only once. They can be read by most DVD-ROM
drives and DVD players. Pioneer released their 3.95
billion byte DVD-R disks in October 1997 and their newer
4.7 billion byte (or 4.38 GB) DVD-R disks in May 1999.
In early 2000 the DVD-R
format was split into a DVD-R(A) "authoring"
version that uses a 635 nm laser and a DVD-R(G)
"general" version that uses a 650 nm laser.
This gives the DVD-R(G) version the future ability to
write DVD-RAM disks. DVD-R(G) is intended for home use
while DVD-R(A) is intended for professional development.
DVD-RW disks can
be rewritten about 1000 times. The disks have a capacity
of 4.7 billion bytes. Pioneer also developed this
format. In 1999 Pioneer released DVD-RW home video
recorders in Japan.
DVD-RAM disks
can be rewritten about 100,000 times and the disks are
expected to last at least 30 years. The storage capacity
is 4.7 billion bytes per side (with one and two sided
disks available). DVD-RAM currently is not compatible
with most drives and players. The first DVD-ROM drive to
read DVD-RAM disks was released by Panasonic in 1999.
Hitachi also released a DVD-ROM drive that can read DVD-RAM
disks.
DVD+RW
DVD+RW is supported by Philips, Sony, Hewlett-Packard,
and others. DVD+RW media will be able to be rewritten
about 1000 times.
AN IMPORTANT NOTE
ON UNITS – GB versus Billion Bytes
A single layer
recordable DVD typically holds 4.7 billion bytes (G
bytes), not 4.7 gigabytes (GB). It only holds
4.38 gigabytes (GB). A double-sided, dual-layer DVD
holds 17 billion bytes, which is only 15.90 GB.
The confusion arises
because the SI prefixes kilo, mega and giga normally
represent multiples of 1000. However, when used in the
computer world to measure bytes these same prefixes
generally represent multiples of 1024 (in the binary
world, 2^10 =1024). This means that a kilobyte = 1024
bytes, a megabyte = 1,048,576 bytes, and a gigabyte =
1,073,741,824 bytes. So 4,700,000,000 bytes = 4.38
gigabytes.
Unfortunately, most DVD
figures are based on multiples of 1000, which means that
your computer operating system and your DVD are using
the same prefix to mean different things. This is an
extremely important distinction to keep in mind when
preparing the files for your DVD.
To make things worse,
data transfer rates when measured in bits per second
are almost always multiples of 1000, but when measured
in bytes per second are sometimes multiples of
1024. For example, a 1x DVD drive transfers data at
11.08 million bits per second (Mbps), which is 1.385
million bytes per second, but only 1.321 MegaBytes per
second. The 150 KB/s 1x data rate commonly listed for
CD-ROM drives is "true" kilobytes per second
(multiple of 1000), since the data rate is actually
153.6 thousand bytes per second.
DVD-Video and DVD-Audio
files and folders
DVDs use specialized
data files which are normally stored in special folders.
Files:
.IFO (Information) Menus and other information about the
video and audio
.BUP Backup files
.VOB (Video Object) MPEG program streams with additional
packets
containing navigation and search information.
.AOB (for DVD-Audio) Similar to .VOB files, but for DVD
Audio disks
Folders:
VIDEO_TS folder This
folder stores the IFO, VOB and BUP files
AUDIO_TS folder DVD
Audio folder which stores the AOB files
Note: the AUDIO_TS
folder is needed for compatiblity with DVD-Video
Players.
When you create the DVD
files you will usually create the following files in
your Video_TS folder:
Video_ts.ifo and
Video_ts.bup The control data needed to navigate the
entire DVD
Vts_01_0.ifo and
Vts_01_0.bup The control data needed to navigate movie 1
Vts_01_0.vob The video
for movie 1, segment 0
Vts_01_1.vob The video
for movie 1, segment 1
etc., up to 9 segments
Vts_02_0.vob, etc. The
video for movie 2, segment 0
etc., with Vts files
for each movie
If you plan to burn a
DVD-R you will usually have to create a DVD-R image file
on your hard drive first. Your DVD Authoring program
should be able to produce the *.img or *.udi file from
your Video_TS and Audio_TS folders. The *.img and *.udi
files are identical except for the file extension, so
you can rename the file using the other extension should
your software require the other file extension.
DVD Creation Tips
TIP: DVD-Video
Content on a CD-R
You can burn DVD-Video
content on a CD-R or CD-RW disk.
The main advantage of
doing this is that you can use an inexpensive recordable
CD rather than an expensive DVD-R. Of course, the
storage capacity of a CD is much less than that of a DVD,
so these "mini DVDs" can only be used for
short programs or for testing.
All but the early
models of DVD-ROM drives should be able to read CD-Rs.
DVD-Video players normally cannot playback DVD-Video
content from a CD-R. You must use a DVD-ROM drive to
play back these CDs.
To make a CD with DVD-Video
content follow your normal DVD authoring procedure until
you have created the VIDEO_TS and AUDIO_TS folders. Then
burn the VIDEO_TS and AUDIO_TS folders to the root
directory of the CD-R or CD-RW.
TIP: Playing Your
DVD-R
If you are having
trouble playing your newly burned DVD-R on a DVD Player
keep in mind that older DVD Players may not be able to
play DVD-R disks. Newer 3rd generation DVD Players
should have no problem.
With a DVD-ROM drive on
a Mac you may need to upgrade your operating system to
MacOS 8.6 or higher before you can play a DVD-R disk.
Once you have used your
DVD Authoring software to create the Video_TS and
Audio_TS folders you will probably want to test your DVD
navigation. Note that even though the files you have
created are on your hard drive you must still have a DVD-ROM
drive installed before you will be able to play back the
files. You must also have DVD player software installed.
DVD player software is always powered by an MPEG
decoder. The decoder can be hardware based, such as the
RealMagic Hollywood+ PCI card (www.sigmadesigns.com/realworld.htm),
or software based, such as DVD Player by Ravisent (www.ravisent.com)
or WinDVD by InterVideo (www.intervideoinc.com).
TIP: Selecting
Your Text – Font and Size
When you are creating
your menu background you will often want to include
text. For example, you will probably want to label the
buttons you create so that the viewer knows what each
button does. Fonts that look ok on a computer screen may
flicker on a video monitor or TV. You should avoid thin
text. About 18 point text is the smallest text that you
should use. Avoid high contrast between your text color
and the background color. Do not use overly saturated
colors as they will "bleed" on a TV screen.
TIP: Video Safe
Area
Most TV screens do not
show an entire video image. The edge of the picture is
normally outside the screen. This allows sets that are
aligned slightly differently to still show a picture
that fills the screen. In order to be sure that the
buttons and text on your menus will be visible to all
viewers do not place them too close to the edge of the
image.
TIP: Making
Bitmaps or "My circles look like ovals"
(square pixels vs. rectangular pixels)
You will often make
your Menu backgrounds in a paint program on your
computer. If you make a perfect circle on your computer
screen, and then you show it on your TV or video
monitor, it will look like an oval. That is because the
pixels on your computer screen are square, while the
pixels on your video monitor or TV are rectangular. In
order to avoid this slight distortion you can make your
images at 720 x 540, and when the image is complete you
can re-size it in your paint program to 720 x 480 (NTSC)or
720 x 576 (PAL). Of course, then your circles will look
like ovals on your computer screen, but they will be
perfect circles on your TV or video monitor.
TIP: Calculating
File Sizes for DVD
Before you spend a lot
of time authoring your DVD it is very important to
calculate your file sizes. Here is a guide to help you
with your calculations.
There are two types of
DVD-R discs, 4.7 GB and 3.95 GB in capacity. Note that
DVD sizes are given in SI units, which means that 4.7 GB
= 4,700,000,000 bytes or 4.7 billion bytes. However,
your Windows operating system uses the computer
convention, where:
1024 bytes = 1 KB and
1024 KB = 1 MB and 1024 MB = 1 GB.
Your operating
system will see a 4.7 GB DVD-R disc as having a capacity
of 4,700,000,000 bytes/ (1024 B/KB x 1024 KB/MB x 1024
MB/GB) = 4.38 GB.
Also note that MPEG2
data rates are often given in Kbits/sec, where 1 Kbyte =
8 Kbits.
Uncompressed audio
sampled at 16 bit, 48 kHz, stereo = 187,500 bytes/s =
1,540,000 bits/sec
Typically MPEG1 Layer 2
audio may be compressed to 224 Kbits/sec (approximately
7:1). At a compression of 384 Kbits/sec the audio is
compressed at approximately 4:1.
An MPEG2 video bit rate
of 6000 Kbits/sec or less generally appears lossless.
At a typical bit rate
of 6000 Kbits/sec for video and 1540 Kbits/sec for one
stream of uncompressed audio, for a total bit rate of
7540 Kbits/sec:
Number of Storage
Requirements
Minutes
10 550 MB Note: The
storage capacity of a CD is 650 MB
15 830 MB
30 1.6 GB
45 2.4 GB
60 3.2 GB
75 4.0 GB Note: The
storage capacity of a DVD-R is 4.38 GB
Keep in mind that the
MPEG2 and audio files must be processed into a VOB file.
A typical Video_TS folder will include .vob, .bup and .ifo
files. The main VOB file (or files, if there are 2 or
more movies) which includes the MPEG2 video will be the
largest file. The other files combined will generally be
much smaller (typically only a couple of MBs).
TIP: Preparing
Your Computer's Hard Drive
When you are burning a
DVD-R it is crucial to maintain the data rate required
by the burner. While this data rate is only about 6 –
10 Mbits/sec, a badly fragmented drive may have data
flow "hiccups" that can cause the data rate to
drop, ruining the DVD-R you are burning. To be safe,
always store your final DVD files on a separate hard
drive, or a separate partition on a hard drive, that you
can re-format prior to creating your final DVD files.
That way you can be guaranteed that your data stream
will not be interrupted because of a fragmented drive.