In most cases you can use the default audio bitrate of 64k. If you need quality stereo sound, use 128k or 192k. For home DVD systems use up to 320k, assuming that your source video has appropriate audio quality. Bit rate/filesize mapping is simple. The size of the audio stream is the audio bitrate multiplied by the duration and divided by 8: size (bytes) = bitrate (bps) * duration (sec) / 8 .
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