The --with-lame is important if you want to process mp4s.
Might want to consider putting some kind of progress indicator (simple polling on tmp_audio_in.u8 vs tmp_audio_out.u8). I ended up looking at the output directory with
watch -n .5 ls -la /tmp/audio_shop-DIRECTORY
I think the cleanup isn't working quite right, getting a rm unlink failure.
I just finished adding video support (and stubbed out audio support).
Due to already using ffmpeg for image manipulations, this turned out to be rather easy.
Give it a try using something like this: