DVD Demystified

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billions of bytes and gigabytes. The operating system will report file sizes in
gigabytes, but DVD capacities are usually given in billions of bytes (see
Chapter 1.) Don’t forget to leave some room for the directory entries.
When adding up file sizes, use the actual file size, not the “size on disk”
value, since the space taken on the hard disk is dependent on the block size.
But likewise, space taken up by each file on a DVD can be more than the
actual file size. For a very tight bit budget, adjust the size of each file by the
DVD sector size: divide the file size in bytes by 2048, round up, then multiply
by 2048. This will give the sector-adjusted file size, which represents the
true amount of space the file occupies on the DVD.
Creating a DVD-9 is not as simple as it might seem. You need two DLTs,
but simply dividing your project in half and creating two disc images will
not work. A DVD-9 has a single UDF bridge directory section located on the
first layer that references files on both layers. If you use formatting software
to create two images, you will get two volumes, each with its own
directory section. The first layer will work fine, but the second layer will be
inaccessible. Use a DVD authoring application or a DVD-ROM formatting
utility that knows how to create DVD-9 images, preferably one that lets you
specify where the layer break occurs.
AV File Formats
Chapter 12
When creating a multimedia DVD for playback on PCs, you have essentially
three choices for the AV format: DVD-Video files (.vob), MPEG files
(.mpg), or computer-oriented media files (.avi, .mov, .mp3, and so on). The
advantages of using DVD-Video content are that the disc will also play in
standard DVD players, the features of DVD-Video such as angles, seamless
branching, fast chapter access, and subpictures are available, and the video
will be more compatible with PC decoders, which are oriented more toward
DVD than MPEG-2. The advantages of using MPEG-2 program stream files
are that you don’t have to use a DVD-Video authoring system; you can easily
create and test playback. You can also make each video clip a file with a
meaningful name rather than trying to find the right access point in the
middle of a .vob file.
The advantages of using other formats are that the development tools
are simple, widely available, and often inexpensive. Since the data rate of
most DVD drives is at least equivalent to an 18x CD-ROM drive, high data
rates can be used with codes such as Cinepak, Sorensen, and Windows
Media Video (MPEG-4) to provide surprisingly good video. It may also be
much easier to create discs that work on both Windows and Macintosh com-