I had converted my entire 5.1 flac collection to Apple Lossless mp4 for playback through the AppleTV (you could simply load the multichannel mp4's into iTunes and play them back using Home Sharing through the Computers app in tvOS 11 and tvOS 12.
But there is a stupid bug and if you play a 5.1 .mp4 it is down mixed to stereo.
If, however you play a video with a 5.1 ac3 audio track, it switches the output to 5.1 and 5.1 mp4s played after that play just fine (stereo audio files also play fine albeit being output as 5.1 with just the two fronts active).
Next time you play a stereo video the output mode switches back to stereo and future 5.1 mp4's are down mixed again.
Stupid mess. I reported the bug early in the beta cycle, but as usual I'll probably have to wait another year before things work again.
By the way, the method to create these 5.1 apple lossless files is to convert a flac using xAct and then rename the resulting .m4a file to .mp4. Those can be added to iTunes and played back just fine (albeit at 16/48 5.1) through Home Sharing.
But there is a stupid bug and if you play a 5.1 .mp4 it is down mixed to stereo.
If, however you play a video with a 5.1 ac3 audio track, it switches the output to 5.1 and 5.1 mp4s played after that play just fine (stereo audio files also play fine albeit being output as 5.1 with just the two fronts active).
Next time you play a stereo video the output mode switches back to stereo and future 5.1 mp4's are down mixed again.
Stupid mess. I reported the bug early in the beta cycle, but as usual I'll probably have to wait another year before things work again.
By the way, the method to create these 5.1 apple lossless files is to convert a flac using xAct and then rename the resulting .m4a file to .mp4. Those can be added to iTunes and played back just fine (albeit at 16/48 5.1) through Home Sharing.