archives: MP4 notes
MP4 supports MPEG2, but not AC3 or DTS. Have to use AAC for audio. At least on paper, ffmpeg supports it fine, as does mplayer, but if you want it properly standardized for full portability, don't use it.
According to wikipedia, MP4 supports AAC, MP3, MP2. I've only had consistent success encoding to AAC. Some MP3 playback is just garbage.