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.