mp4 videos AAC 5.1 -> AC3 (quickest audio encode?)

[alexeliasson]

Friends,

I have a number of .mp4 videos encoded with 5.1 (6 Channel) AAC audio. I would like to end up with an .mp4 with AC3 5.1 and 2 channel AAC encoded for Dolby Prologic II (such as the way Handbrake will do when encoding a video using AC3 passthough). I do not need to re-encode the video.

I stress that I don't want to reencode the video, only adding the AC3 5.1 track from the current AAC 5.1 track.

If I hit the "ATV3 Specs" alternative in Handbrake every movie takes about 1.5h to re-encode (it re-encodes everything).

Any ideas? Tried mkvtomp4 but it can only ac3 -> aac and not backwards. That's a shame because I love that program, and it's so fast.

[jagabo]

Do you realize that many programs and media players can't handle AC3 in MP4? And you're only going to reduce the quality by reencoding to AC3?

[alexeliasson]

Hi!

Thanks, and to your question: yes. However, I'm on a Apple TV 3 setup and I need that specific audiotrack configuration to get a surround 5.1 sound

Any ideas?