Adding AC3 Dolby Digital 5.1 multichannel audio to an MP4 without re-encoding

I recently “obtained” some video files which had 5.1 surround sound encoded as AAC, but AppleTV does not play multichannel audio in AAC format.

While AppleTV can play back stereo or Dolby Pro Logic II in AAC format, it requires multichannel audio be encoded as AC3. None of these “acquired” MP4s have AC3 5.1 6-channel audio!

I could encode the file again, but that takes to much time. Is there a way I can just add or import AC3 multichannel audio to my existing video files?

The short answer is yes.

Continue reading