Apple TV, receiver and ATSC 3.0 AC-4 audio question

[oshogg]

Hi,

I just ordered HD HomeRun Flex 4K and am expecting to receive it in a day or two. I am planning to use it with Apple TV 4K (latest gen) connected to Denon avr-x3700h receiver via HDMI. I have a 9.2 surround speaker system in the home theater driven by the Denon receiver. Will Apple TV 4K be able to pass AC-4 to Denon receiver and will it play with all speakers? Or, would that be converted to 2.0 stereo with cloud-based AC-4 decoding?

Thanks,
Osho

[nickk]

Unfortunately Apple does not support AC4 passthrough (or even AC3 passthrough) on Apple TV.

For the moment that means ATSC 3.0 channels use the cloud transcode service and delivered in stereo.

Nick

[sdust]

For the moment that means ATSC 3.0 channels use the cloud transcode service and delivered in stereo.

Can you clarify how does it work? ffmpeg shows 5.1 channel present when asking for ATSC 3.0 channel

Code: Select all

$ ./ffmpeg -i http://172.31.31.33:5004/auto/v104.1

Input #0, mpegts, from 'http://172.31.31.33:5004/auto/v104.1':
  Program 3
  Stream #0:0[0x31]: Video: hevc (Main 10) ([36][0][0][0] / 0x0024), yuv420p10le(tv, bt709, progressive), 1920x1080 [SAR 1:1 DAR 16:9], Closed Captions, 59.94 fps, 59.94 tbr, 90k tbn
  Stream #0:1[0x32](spa): Audio: ac4 (AC-4 / 0x342D4341), 46034 Hz, stereo, fltp
  Stream #0:2[0x33](eng): Audio: ac4 (AC-4 / 0x342D4341), 46034 Hz, 5.1(side), fltp
  Stream #0:3[0x39](eng): Data: bin_data (STPP / 0x50505453)
  Stream #0:4[0x3a](spa): Data: bin_data (STPP / 0x50505453)

[kyl416]

Can you clarify how does it work? ffmpeg shows 5.1 channel present when asking for ATSC 3.0 channel

That's because you're using a custom ffmpeg build that has the unofficial AC-4 patches, until those patches are integrated into mainline ffmpeg with a license that allows for commercial redistribution, it can't be used for app store builds.

Apple TV itself doesn't natively support AC-4, so the HDHomeRun app has to use Silicondust's cloud transcoding, which in its current form only outputs stereo.

[oshogg]

OK, thanks for the update. This is sad.

[pdicamillo]

I have an HD HomeRun Flex 4K and an Apple TV 4K box. I recommend using the Channels app with the Apple TV. The app isn't free, but it works very well. It either decodes the AC-4 audio itself, or if decodes AC-4 using a remote server it's transparent. My receiver shows the audio output from the Apple TV for the ATSC 3.0 channels as 5.1 channel PCM.