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Playing AAC multichannel (5.1 surround) audio stream on Apple TV

I have a tvOS app that receives AAC 5.1 audio stream over the network and I am using AudioToolbox to decode (mFormatID = kAudioFormatMPEGAAC) to 5.1 channels. But I only hear 2 channels (Stereo) outputs on my 5.1 surround system (which is connected to the TV using an Audio Optical cable).


I am not sure why PCM multi-channel is not outputting from AppleTV. Am I missing anything?

Posted on Jun 8, 2021 9:02 AM

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Question marked as Top-ranking reply

Posted on Jun 8, 2021 2:29 PM

I have a tvOS app

Are you programming an app? Then consider visiting the developer forums.


Setting manually to Dolby Digital 5.1 did not help. I think it says it could be re-encoded to DD 5.1 or Stereo.

DD 5.1 and Stereo are fallback; that is how it is supposed to work.


So it might not do re-encoding. I am not sure how to force to re-encode.

I think it re-encodes everything, possibly with exception of what already matches the set output format.


If I want to play 5.1 AAC audio, what should be set up if not optical cables?

AAC 5.1 would be converted to Dolby Digital 5.1, with the Dolby Digital 5.1 output setting. There is no untouched passthrough, AAC or otherwise. Either uncompressed PCM Multichannel (over HDMI), re-encoded Dolby Digital 5.1, or downmixed Stereo (PCM 2.0). Those are device settings, not app settings.

4 replies
Question marked as Top-ranking reply

Jun 8, 2021 2:29 PM in response to aakarfromtoronto

I have a tvOS app

Are you programming an app? Then consider visiting the developer forums.


Setting manually to Dolby Digital 5.1 did not help. I think it says it could be re-encoded to DD 5.1 or Stereo.

DD 5.1 and Stereo are fallback; that is how it is supposed to work.


So it might not do re-encoding. I am not sure how to force to re-encode.

I think it re-encodes everything, possibly with exception of what already matches the set output format.


If I want to play 5.1 AAC audio, what should be set up if not optical cables?

AAC 5.1 would be converted to Dolby Digital 5.1, with the Dolby Digital 5.1 output setting. There is no untouched passthrough, AAC or otherwise. Either uncompressed PCM Multichannel (over HDMI), re-encoded Dolby Digital 5.1, or downmixed Stereo (PCM 2.0). Those are device settings, not app settings.

Playing AAC multichannel (5.1 surround) audio stream on Apple TV

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