Help! Xvid audio sync issues when encoding audio to mp3
 

I'm using Sony Vegas to encode a video file to Xvid. In my choice of audio formats, I can select from among MPEG Layer 3, PCM Uncompressed, or a bunch of crummy low bit rate codecs. When I choose the mp3 option, after encoding the audio gradually leads the video by about 3-5 seconds per half-hour. When I choose PCM, the audio stays synched, but the file size is many megabytes larger.

Is there some way to add more audio format choices to the list in the compression template? Is there anything else I can do to get good audio compression without having sync problems when encoding to an Xvid AVI?

My source file is an NTSC video file captured to MPG (MainConcept MPEG Video, Cyberlink audio) using Roxio Media Import.

Abandoned this method of encoding. Encoding to H.264 mp4s now. Works much better, audio stays in sync. But now I have a problem of those files crashing Windows Media Player. See my post to this thread.