For my own future reference when trying to re-encode video (to a dumber mpeg4 implementation for my linkplayer2) with multiple audio tracks all at the same time:

ffmpeg -i 1x01\ Space\ Pilot\ 3000.avi -f avi -vcodec divx -b 1133k -acodec mp3 -ab 128 output.avi -acodec mp3 -ab 80 -newaudio

Be sure to verify video playability, quality and audio sync.

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