The source is an ISO file, so there is no DVD h/w involved. The ISO itself plays with the audio perfectly in sync. Most all converted ISO’s have audio perfectly in sync. Ratatouille and Zathura have both been consistant problems. Zathura now works when using single pass mode, but not two-pass. When in two-pass mode for Zathura there is a long silent period near the start of the movie, and the audio is then out of sync by that amount.
Most all other conversion tools also have problems with Zathura, excepting iriver’s own conversion tool, which does produce a converted movie that is perfectly in sync (though the video is of poor quality).
Is it possible whatever mp3 audio encoder you use would have a delay only on certain movies? Seems odd.
The resulting converted movies are tested both on a PC and on a clix gen2 device (when conversion actually allows playback on the device, which is another issue). Both play out of sync in the same manner.