Media player won't ouput 6 channel audio from some AC3/AAC sources

I have my AppleTV plugged into my receiver using a toslink cable and the receiver is Dolby Digital 5.1 compatible. ATV Flash and media player are updated to the most recent versions. All of my media is on a network share, and all of it is 720p x264 video, with AC3/AAC 5.1 audio, in a Matroska container. I have the AC3 enabled in the media player settings, DTS is disabled, however I don’t have any media using the DTS codec. The AppleTV sound output is set to auto.

For the most part all of my media delivers a true dolby digital 6 channel signal to my receiver as expected and it sounds fantastic. However I have come upon a couple of movies that do not deliver a dolby digital signal at all, 5.1 or stereo. Instead all I get is a standard stereo signal.

I have inspected these movies with VLC on my computer and there definitely is a 6 channel AAC/AC3 stream included inside these files. I can’t seem to find any solid difference between the movies that do output DD 5.1 and the ones that don’t.

After further investigation I’ve realized that every movie with AC3 encoding outputs the 6 channel audio just fine. However only about 25% of the movies I have with AAC encoding will out the 6 channel audio signal.

This is confusing to me… how can some 6 channel AAC encodes work fine and some not?

Also, this only happens on my AppleTV using media player… none of my files have an issue outputting a 6 channel output on my computer.

I was mistaken again. Media Player was showing AAC as the audio codec, but that’s because I had to reload the meta data.


So… the final conclusion is that ATV Flash will not output 5.1 audio from an AAC source. All of my AC3 sources work as expected.

Currently MP will only support AC3 and DTS passthrough. AAC audio tracks will be down sampled to 2ch stereo.

Furthermore, most receivers won’t support 6CH AAC sound, so we’re hoping to add some kind of way to transcode the AAC audio to AC3 in order to get full surround sound for these files.

Thanks for the reply James! I figured this was the case, just wanted to make sure.

Adding transcoding for AAC would be amazing! Currently I have to use a program to encode any 6CH DTS audio into 6CH AC3 because my receiver doesn’t support DTS. Which isn’t too hard, I found a program that will do it. However I haven’t been able to find a program to transcode AAC into AC3 for OS X, so I have to try to avoid those files.