DVDs contain the audiostream in a format introduced
by Dolby Laboratories. This encoding is called AC3
(or Dolby Digital) features 5 discretely encoded
channels which (in comparison to Dolby Surround)
have full bandwidth and are not matrix encoded into a two
channel system.
As with the video-part of a DVD this audio-format
takes up quite some space on the DVD, so to have as much
bitrate as possible available for the video we can
decode the audio and then re-encode it to MP3
or OGG Vorbis. Which save a lot of space and on normal
home-stereos will sound okay. (if you have an AC3
receiver you may consider muxing AC3 into the
AVI).
But if you're low on space you should re-encode to MP3.
There are two good quality ways possible to decode the AC3-stream.
