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5.1 PCM plays as stereo

tvOS Video playback support subforum
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cosmoxl
Posts: 1759
Joined: 12 Dec 2015, 14:16

5.1 PCM plays as stereo

Post by cosmoxl »

The first problem I've encountered with MrMC. :D

Blu-ray transode with an AAC 5.1 track from the DTS-HD track, in handbrake, using avcodec.

The DTS-HD and DTS tracks passthrough to my denon receiver as expected. But, the AAC 5.1 track outputs as stereo.

Other software (Air Video HD on ATV4, Kodi on PC) playback the AAC 5.1 properly.

Is this a known problem? Thanks!
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davilla
Team MrMC
Posts: 4377
Joined: 26 Oct 2015, 17:01

Re: 5.1 PCM plays as stereo

Post by davilla »

No known amp/receiver can decode any form of AAC, I've looked for them before. So right now, AAC 5.1 gets decoded internally and down mixed to 2 ch PCM. The tvOS can output 8 channels of PCM but under iOS, there is only two channel PCM. As the port is based off iOS audio handling, channels are fixed to two.

You might enable ac3 transcode, I'd have to poke into the code but this might transcode AAC 5.1 to AC3 5.1.

This will change in the future but we have a few things to deal with, one being there is no API to fetch the details on if the atv4 is connected to a dumb hdtv or via a multichannel receiver.
cosmoxl
Posts: 1759
Joined: 12 Dec 2015, 14:16

Re: 5.1 PCM plays as stereo

Post by cosmoxl »

davilla wrote:No known amp/receiver can decode any form of AAC, I've looked for them before. So right now, AAC 5.1 gets decoded internally and down mixed to 2 ch PCM. The tvOS can output 8 channels of PCM but under iOS, there is only two channel PCM. As the port is based off iOS audio handling, channels are fixed to two.

You might enable ac3 transcode, I'd have to poke into the code but this might transcode AAC 5.1 to AC3 5.1.

This will change in the future but we have a few things to deal with, one being there is no API to fetch the details on if the atv4 is connected to a dumb hdtv or via a multichannel receiver.
Thanks for the great answer.

Of course I knew the AAC gets decoded by MrMC but didn't know this port was limited to stereo after that.

No matter anyway as digital audio gets passed through.
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davilla
Team MrMC
Posts: 4377
Joined: 26 Oct 2015, 17:01

Re: 5.1 PCM plays as stereo

Post by davilla »

It will change :) Count on it as the ATV4 is the 1st iOS based device that can output 8 channel PCM and more.
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