Q: I used iTunes 6.0.2 to convert a video file to one that is compatible with the iPod, but in doing so it has removed the sound track. Why would this be, and is there any way to avoid this?
A: QuickTime Pro and all applications which depend on it (iMovie, iTunes, and several 3rd party conversion programs) simply do not support the conversion video files which are “Muxed,” or multiplexed. This means that the video has been encoded such that the audio and video are stored in a single track, rather than independently.
Unfortunately, muxed MPEG files are fairly common, necessitating for all but casual users one of the third-party conversion utilities which support it. On the Mac, our favorite iPod-specific video conversion utility, Podner, supports muxed audio, as do several options on the PC.
Alternatively, non-iPod specific “demuxing” utilities exist on both platforms, which create an intermediate video compatible with iTunes’ converter.
To determine if the video you’re trying to convert is muxed, open it in QuickTime, and select “Show Movie Info” from the “Window” menu.