I had started using ffmpegX in order to convert a few RMVBs I had into MP4 format so I could play them on my iPod, and received very in-depth help on how to finally make it work. The particular problem with my RMVB files was that ffmpegX was unable to find the audio, so setting it to convert to MP4 always caused it to output .264 files that only had the video, so I had to extract the audio separately and then use MP4Box in the OSX terminal to combine them, then run that file through iSquint so it could be transfered onto my iPod.

Well, I was fine with doing all that for those RMVBs because I was so happy to finally be able to have them on my iPod, but now I find that it wasn't a problem with just those particular RMVB files, but a problem ffmpegX is having with any RMVB file. Needless to say, I wasn't very happy when I found that out.

So, does anyone have any clue at all as to why ffmpegX wouldn't be able to convert directly from any RMVB to MP4?