AC-4 audio output from ATSC 3.0

[DSperber]

I have just acquired an Xiaomi TV Stick 4K, so now I have two Android streaming devices to compare performance of, using my Flex 4K tuner hardware supported by HDHR DVR server engine as well as NextPVR server engine.



And then there's the client comparison, between HDHR app (running on LG TV, ATV4K, Shield Tube, and Xiaomi Stick) and uiDroid app (running on Shield Tube and Xiaomi Stick). Video output from all devices goes through a Yamaha RX-A1080 AVR and then on to an LG OLED C9 TV. Audio output from all devices also goes through the AVR (which obviously does NOT support AC-4 directly, but obviously DOES handle all other audio codec formats).



In particular, right now I am specifically testing with a recording made by NextPVR from an ATSC 3.0 channel (105.1 KTLA HD here in Los Angeles), which absolutely contains AC-4 DD5.1 with all six channels populated with sound.


And I am contrasting audio output from uiDroid running on both Shield Tube and Xiaomi Stick both feeding my AVR, as heard out of the speakers managed by the AVR. Turns out the output from uiDroid on the two devices is quite different. Below are some images of "volume" on all six channels as seen by the AVR. They are not all exactly at the identical instant in time, but they do show approximately what I'm writing about here.



==> uiDroid output for AC-4 5.1 is PCM 2.0 on Shield Tube, and Dolby (MAT) 5.1 at very low volume on Xiaomi Stick.



(1) output audio from uiDroid on Shield Tube is not 5.1 in any form, but is PCM 2.0 and at reasonable volume.








(2) output audio from uiDroid on Xiaomi is Dolby (MAT) 5.1, and is very very low in volume.








(3) for comparision, output audio from LG HDHR app running on LG OLED C9 (and returned to AVR through ARC/eARC), which utilizes locally available built-in Dolby-licensed AC-4 decoding and does "passthrough" of transcoded AC-3 DD5.1).








I am PM'ing you the URL where I've uploaded the actual TS/XML recording files, so that you can use it yourself in uiDroid and hear what I'm hearing (and seeing).

[mvallevand]

You have to understand uidroid is is not a sophisticated player and it relies totally on NextPVR for the GUI and ExoPlayer for playback with some logic to glue them together. SiliconDust seem to tweak their clients for each platform and variety of Android.

1. I can't say how the ffmpeg render works and if the unofficial AC-4 patch for ffmpeg supports multiple channel PCM passthrough. If you don't use passthrough do you get 5:1? I can probably find a copy of ffplay the will output to HDMI to see if it gives 5:1

2. The ratio to the LG looks correct. If you are using CEC for volume turn it off and see if the Android volume settings make a difference. It might be best to use this APK which is the ExoPlayer reference app with AC-4 samples https://www.mediafire.com/file/bafz5sld5...e.apk/file

I will try your sample but my only test is if I hear any sound through the rear speaker.

Martin

[DSperber]

If you don't use passthrough do you get 5:1?

If you are using CEC for volume turn it off and see if the Android volume settings make a difference.    It might be best to use this APK which is the ExoPlayer reference app with AC-4 samples https://app.mediafire.com/wioikyyvci8ap 

Martin

Where are the "passthrough" and "CEC" settings you speak of? In uiDroid? If so, how do I get into Settings in order to view/change them?  Remember, I only have the Shield Tube remote and Xiaomi remote. I certainly have done nothing other than install the APK, so whatever settings there might be as of this moment I have changed nothing from the installation default.

Also, WHICH of these APK files that your URL points to is the one you are suggesting I install?

[mvallevand]

I screwed and gave a list to public files, it should now be a link to the correct file. I definitely hear sound 5:1 sound with this from my Xiaomi 4k

If volume is controlling your receiver or TV you are using CEC if not you are using Android.

Martin

[DSperber]

I screwed and gave a list to public files, it should now be a link to the correct file.  I definitely hear sound 5:1 sound with this from my Xiaomi 4k

If volume is controlling your receiver or TV you are using CEC if not you are using Android.

Martin

Yes, as I said the sound from the Xiaomi IS 5.1: it shows on my AVR as "Dolby (MAT) 5.1".

It is the Shield Tube where the sound from uiDroiid playing the identical recording that is only PCM 2.0.

I think you wanted me to go to the "device preferences" settings on the Shield or Xiaomi, not somewhere in uiDroid. In fact there IS a "passthrough" setting in the "select formats" group of the Xiaomi, and i have it enabled. And I AM getting Dolby (MAT) 5.1 (i.e. LPCM 5.1) to the AVR, which is correct.

It is the Shield where there is no such corresponding "passthrough" setting that I can find. And it is the Shield where the audio going to the AVR is only PCM 2.0.

So, what next?

[DSperber]

it should now be a link to the correct file.  I definitely hear sound 5:1 sound with this from my Xiaomi 4k

Martin

I've now installed this APK for ExoPlayer on the Shield. But I have no idea which of the demo files you want me to play, to see what comes out.

I assume I should be in the "Dolby Audio AC-4 Test" group. But trying, for example, "Multi Channel Audio, Dolby Audio AC-4, On Demand profile" but when I push PLAY on it I get a popup error message saying "media includes audio tracks, but none are playable by this device".

How do I use this, am I in the right group, which file should I use, and why is it giving me this error?

NOTE: all other apps running on the Shield have no problem delivering multi-channel audio to the AVR. This includes DD+ 5.1, Dolby Atmos, etc., and includes Netflix, Hulu, Prime Video, etc., as well as HDHR that delivers PCM 5.1 (although it is really an upmixed stereo returned from their cloud-assisted AC-4 decoding).

Only uiDroid on the Shield is the problem, sending "PCM 2.0" to the AVR from the ATSC 3.0 channel and source AC-4 DD5.1. Using the Xiaomi it sends "Dolby (MAT) 5.1".

NOTE: when I play the ATSC 1.0 version of the channel the imbedded DD+ 5.1 audio delivered by uiDroid running on Shield IS delivered properly as 5.1, and the AVR shows it as "Dolby Digital 5.1".

==> The problem is specifically with uiDroid running on Shield (not Xiaomi, where it is correct), and handling of the ATSC 3.0 channel and the AC-4 audio.

[mvallevand]

That APK shouldn't play on the Shield since it doesn't have AC-4 support. I marked this trial for AC-4 against your item #2 which was the Xiaomi to test the low volume levels so you would be testing the AC-4 streams.

I don't know why you are wasting time comparing with other services that don't use AC-4 For the Shield there is not much I can do, or plan on doing with ffmpeg. Perhaps download Emby for Windows and extract their ffmpeg and see if it can transcode your recordings to 5:1 AC3 and see how those files play via the uidroid Video library.

ffmpeg -i filename.ts -vcodec copy -acodec ac3 output.ts

Note PCM does't have channels the player has to set the number of channels.

Martin

[BrettB]

NOTE: all other apps running on the Shield have no problem delivering multi-channel audio to the AVR. This includes DD+ 5.1, Dolby Atmos, etc., and includes Netflix, Hulu, Prime Video, etc., as well as HDHR that delivers PCM 5.1 (although it is really an upmixed stereo returned from their cloud-assisted AC-4 decoding).
...
Only uiDroid on the Shield is the problem, sending "PCM 2.0" to the AVR from the ATSC 3.0 channel and source AC-4 DD5.1. Using the Xiaomi it sends "Dolby (MAT) 5.1".
...
==> The problem is specifically with uiDroid running on Shield (not Xiaomi, where it is correct), and handling of the ATSC 3.0 channel and the AC-4 audio.

"Other apps running on the Shield have no problem delivering multi-channel audio to the AVR" because their media isn't using AC-4 encoded audio! That is of no use for comparison to ATSC 3.0 broadcast streams.

What exactly are you expecting from the Shield Tube with AC-4 audio? The Shield Tube hardware doesn't support AC-4 decoding, so it won't be able to process those audio tracks. And you stated that your AVR hardware also doesn't support AC-4 decoding, so even if the Shield Tube hardware was operating in passthrough mode for AC-4 audio and sending the raw AC-4 stream to the AVR, the AVR still wouldn't be able to decode it either.

Uidroid doesn't directly do any audio processing. It uses ExoPlayer which in turn uses the underlying Android o/s and hardware.

I would expect that on the Shield Tube (and your AVR) having no AC-4 support, you would not get any audio with an ATSC 3.0 stream. But, from what you are describing, it sounds like the new version of ExoPlayer may be trying to use ffmpeg to software decode the AC-4 audio to PCM format when there is no other alternative (rather than just not giving any audio).

[mvallevand]

Brett, uidroid uses an unofficial ffmpeg patch to get AC-4 sound on any Android device. I have now idea if that patch delivers 2:0 or 5:1 sound (AC-4 can have 17 objects, they aren't even channels anymore) but it is a not a full implementation of AC-4. This is why I asked for the test with Emby's ffmpeg.

I know in ExoPlayer ffmpeg output is always PCM but I don't know how or if I can force decoding multiple channels. I do know that the even if I could there is no functionality in UI client to tell me to do this. The whole Android audio chain is also a bit of mystery, since my BT soundbar doesn't work with native ATSC AC3 output on some of my Android players but it works on others.

Martin

[BrettB]

Brett, uidroid uses an unofficial ffmpeg patch to get AC-4 sound on any Android device.  I have now idea if that patch delivers 2:0 or 5:1 sound (AC-4 can have 17 objects, they aren't  even channels anymore) but it is a not a full implementation of AC-4.  This is why I asked for the test with Emby's ffmpeg.

Martin: Does uidroid always use ffmpeg if there is AC-4 sound or only if the hardware doesn't have support for it?