H264 with AC3

Question

Hi,
I would like to export my FCPX HD videos using H264 video and AC3 5.1 multichannel audio in an appropriate container.
The reason why I am not using AAC multichannel audio is because:
- AppleTV does not support true multichannel AAC decoding (or transcoding to DTS, as recommended by the DVB);
- DVD or BlueRay burning software do as well not support multichannel AAC (just performing downmixes);
I made tests on Compressor doing seperate H264 and AC3 encodes, then mux'ing both components into one MP4 stream. Unfortunately, although QT, VLC as well as ATV can decode the stream, no disc burning software will accept this 'non-standard' component combination.
My questions:
- Is there a possibility within compressor to combine H264 video with AC3 audio in a appropriate container ?
- Is anybody aware of a DVD or BlueRay burning software capable to handle multichannel AAC as true multichannel (whether as discrete PCM channels or as an AC3 transcode) ?
- Are there plans that ATV4 will properly support AAC multichannel (whether as discrete PCM channels via HDMI or as a DTS or AC3 transcode via optical audio interface) ?
Thank you

Answer 1

I think I found the solution:
I inspired myself on the iTunes format .m4v which allows the combination of H264 video with AC3 audio.
Consequently there are several ways to proceed:
- export via FCPX using ProRes 422 and 5.1 PCM linear audio, then ecoding to H264 and AC3 using e.g. handbrake;
- export via FCPX trhough Compressor using seperate encodes for H264 and AC3, then muxing both compoents into a .m4v file using a mux tool such as Subler.
.m4v is indeed recognized by ATV, as well as by DVD/BD bruning software such as Toast.
a few points thought which I would recommend Apple to considered:
- Compressor should allow to directly create a .m4v file with H264 video and AC3 audio (currently not possible)
- Quicktime should be updated to correctly display within inspector the status of the AC3 decode. Indeed, presently quicktime will decode a 5.1 AC3 but will display it as a 'stereo' audio, which is not correct and misleading. VLC shows for instance the correct Dolby format...
- it's a pitty that iDVD does not support AC-3 passthough or a transcode for AAC to DTS or AC3, because multichannel audio is quite standard for DVD's and most MAC users will have video files with multichannel audio.
- ATV should support multichannel decoding of .mov files using multichannel AAC, whether via discrete PCM channels on the HDMI interface or via a DTS (or AC3) transcode via the optical audio interface.
Thx and best regards
Steve