Audio supported in mp4 container for TivoHD

txporter · 11-03-2009, 01:51 PM

I am trying to understand what audio can be placed in the mp4 container and play correctly on a TivoHD. For my particular setup, stereo is fine since I do not have a surround sound setup. However, I don't mind sending 5.1 audio up to my tivo as long as it plays correctly.

Recently, I was converting some Rescue Me episodes from DVD with XVID4PSP (normally I use Handbrake, but Rescue Me only has captions. I always burn in subs, but Handbrake cannot currently handle .srt files.). The audio track from Rescue Me went from 2ch to 6ch between Seasons 1 and 2. When I pushed the resultant mp4s from Season 2, I was only hearing the sound effects and some of the music, but no voices. XVID4PSP was converting the sound to AAC but keeping the # of channels.

I didn't try setting my audio to output to PCM (or whatever its called), but upon further reading I think that might have been a workaround for me. I did try pulling the videos rather than pushing them and they were converted to mpg2 with 6ch sound (I believe also AAC, but I don't remember exactly). Those played fine.

So does 6ch AAC not work in the mp4 container? Does 6ch AC3? I can force XVID4PSP to mix down to stereo, but it is an extra step that I would like to avoid if possible. I might be able to do a direct copy in XVID4PSP to keep the 6ch AC3 if that will work. I can try some of this out myself later when I get time at home, but I was hoping that some folks here have already gone through this and already know what TivoHD supports for audio in the mp4 container.

moyekj · 11-03-2009, 02:06 PM

video_compatibility lists what is known to work. If you really want true surround sound you have to use multi-channel AC3 audio. Even though multi-channel AAC audio does push to the TiVo I don't believe you will get true multi-channel audio out of the TiVo unless you use AC3 right now. i.e. What you want is mp4 container with H.264 video & AC3 audio for highest quality mp4 native push to S3 Tivos.

ALSO NOTE: Many media players don't actually support playback of AC3 audio in mp4 container since that is relatively new addition to the spec of what mp4 containers support. However players such as Videolan VLC can play them as of course can S3 Tivos.

txporter · 11-03-2009, 02:16 PM

Thanks, Kevin. I should have thought to look in the streambaby docs. Did some searches here and looked through pytivo stuff. I just realized that was likely the problem when I started the post here.

Just out of curiousity though, do you know if changing the audio output to PCM would have forced the channels all to stereo or is 6ch AAC simply borked on Tivo?

moyekj · 11-03-2009, 02:49 PM

Not sure about PCM. If your receiver supports it might be worth a shot. I doubt it sounds as good as real AC3 though.
BTW Netflix streaming also suffers because of this problem. While Netflix audio could be multi-channel WMA (WMA Pro) it wouldn't do much good because I don't think Tivo can put out multi-channel WMA and even if it could there aren't that many receivers out there that support it anyway. That's why at least for now Netflix streaming is relegated to stereo.