If utilities on which tovid depends (ffmpeg, transcode, mplayer) are built without the a52 flag set, videos which are converted by tovid will lack audio. This is not a tovid bug per se, but it might be useful to add this info to the ebuild. Reproducible: Always Steps to Reproduce:
Hmm are you really sure that this happens in general? I mean are you sure that every video lacks sound (even videos which are not using a52-codec at all?) when you merged ffmpeg, transcode and mplayer without the a52-support? To me this sounds more like you tried to convert a movie with a52-audio using tovid, without having the proper codecs installed.
It happened on several avi's that I tried to convert, and I believe they all used a52-codec. I have converted flash files to mpg successfully with audio, so I'd guess your analysis is correct.
Thought so ;) So this bug-report can be closed.