Using the calculated bit rate – Apple DVD Studio Pro 4 User Manual
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• Subtitles: The amount of space required by subtitles can vary widely, depending on
how many of the 32 streams you use, the type of content you use (simple text characters
or full-screen graphics), and how often you change them (several times a second, or
more typically, once every four or five seconds).
Simple subtitles average about 10 kbps—roughly 2 megabits of space per hour, which
is negligible on most titles. If you intend to use subtitles more as an animation tool,
with full-screen graphics that change often, you must make significant allowances for
them. (The maximum bit rate allowed for a subtitle stream is 3.36 Mbps—almost as
much as the video stream.)
• Transitions: The amount of disc space required by each transition varies depending on
the transition’s length and type. In general, for SD projects, which use a bit rate of
6 Mbps for transitions, you should allow 750 KB of disc space for every second of
transition time in the project. For HD projects, which use a bit rate of 20 Mbps for
transitions, you should allow 2.5 MB of disc space per second.
Note: Keep in mind that adding a transition to a menu results in a separate transition
clip for each button—a menu with 18 buttons can require 18 transition clips.
Unless you are using an exceptional number of stills, menus, or subtitles, you can usually
account for the amount of space required by these items by allowing a five percent
overhead. The easy way to apply this overhead amount is to multiply the bit rate you
have figured out by 0.95. In the earlier example, the DVD-5 disc bit rate drops from
3.77 Mbps to 3.58 Mbps; the DVD-9 bit rate drops from 7.65 Mbps to 7.27 Mbps.
Important:
It is much better to be conservative and find yourself with some disc space
left over than to get to the end of the project and find it will not fit on the disc.
Using the Calculated Bit Rate
The bit rates you calculate can be used as the bit rate entry of your encoder, regardless
of the encoding method you intend to use (one pass, one-pass variable bit rate [VBR], or
two-pass VBR). See
for more information.
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Appendix C
Calculating Disc Space Requirements