Apple DVD Studio Pro 4 - Manual (Page 40)

Beware of Setting Your Bit Rate Too High
You will find that with some DVD projects, the content easily fits on the disc, and you
may be tempted to use the highest video bit rate available. While higher bit rates produce
better quality, you must take into account other factors before deciding to use the
maximum allowable value.
The maximum video bit rate allowed on SD-based DVDs is 9.8 Mbps, but rarely is that
practical to use because DVD players support combined video, audio, and subtitle bit
rates of up to 10.08 Mbps. For HD-based DVDs, the maximum video bit rate is 29.4 Mbps
for HD assets and 15.0 Mbps for any SD assets used in an HD project, with an overall
maximum bit rate of 30.24 Mbps.
In practice, you should be conservative when determining how high of a bit rate to allow
for. Trying to squeeze out the highest possible bit rate for your project can lead to player
compatibility and disc space issues.A general recommendation is to not exceed 9.2 Mbps
for the combined video and audio bit rates when authoring SD projects or 29 Mbps when
authoring HD projects.
Important: If you are building your project and DVD Studio Pro detects that the bit rate
of the multiplexed stream is too high, the build stops and an error message appears.
Using PCM or AC-3 Audio
A single PCM audio stream using typical settings (as produced with the embedded AIFF
encoder) requires 1.536 Mbps, which leaves an absolute maximum bit rate for the video
in an SD project of around 8.54 Mbps. If there are two PCM audio streams, 3.07 Mbps
must be allowed for the audio, leaving just 7.01 Mbps for the video.
Note: Even though you can only play one audio stream at a time, the bit rates of all audio
streams must be added together when determining the overall bit rate for a track. Similarly,
all subtitle streams must be added together and added to the overall bit rate.
Using AC-3 audio in place of the PCM audio leaves far more room for the video bit rate.
Stereo AC-3 audio using typical settings requires only about 224 kbps—using two stereo
AC-3 streams in place of the PCM audio leaves about 9.6 Mbps for the video.
See Calculating a Project’s Disc Space Requirements for more information about allowances
for other audio formats.
Subtitle Allowances
Subtitles generally use a very small bit rate—about 10 kbps per stream. Larger subtitles
that change frequently or use graphics can have a significant impact though and can
affect the maximum bit rate you can use for the video.
40 Chapter 2 Planning Your Project