AC4 Support in Kodi on NVidia Shield?

[cncb]

I am trying out ATSC 3.0 with the HDHR 4K and I thought I would get AC4 audio support via passthrough on my NVidia Shield to my Denon AVR.  But I get no sound - it doesn't even recognize an audio track in Kodi.  Is there a setting somewhere that I am missing or is this not supposed to work yet?  I do get audio with the HDHR app.

[mvallevand]

Given Kodi's ffmpeg doesn't recognize AC-4 it is not expected to work. Try uidroid, it can decode AC-4 using ffmpeg patches on Android and if you configure pass AC-4 audio passthrough on Android it should also work but this is untested. If your player supported native AC-4 it would also work but I don't think the Shield does.

Silicon Dust did tell me that the current ffmpeg patches for AC-4 might not give the full range of AC-4 so uidroid and Emby could be impacted. I would be interested in reading your audio comparison evaluation

Martin

[cncb]

Thanks, I get sound with uidroid. It decodes to PCM even if the ffmpeg audio option is unchecked, so no passthrough. They only seem to be broadcasting 2-channel audio at the moment which the HDHR app seems to somehow convert to multichannel DD which sounds pretty bad and I prefer the ffmpeg implementation.

My ATSC 1.0 reception has gone to crap lately, so I was hoping to resolve this with the ATSC 3.0 channels. It doesn't seem to be quite ready yet so I might just suck it up and pay for more than we need in Youtube TV...

[mvallevand]

Thanks for testing, it wouldn't be the ffmpeg setting. You would have to tell Android to be able to pass through AC-4 and ExoPlayer would need to identify that your device had AC-4 compatible codecs so that it didn't invoke ffmpeg. I have only seen the codecs on phones themselves, but I thought this might be a way.

Martin

[DSperber]

I have installed "Kodi AC-4" (a personal GitHub project from a very talented guy) on my Win7 and Win10 systems, each of which has NextPVR server installed and therefore usable as the standard Kodi backend. And having bought a Silicon Dust HDHomeRun Flex-4K tuner, thereby had support for all its tuners in NextPVR... and by extension in Kodi AC-4... for the new ATSC 3.0 channels rolled out recently here in Los Angeles.

https://forums.nextpvr.com/showthread.ph...#pid566586

Kodi AC-4 uses the modified Windows FFMPEG which has built-in support for AC-4. And it works.

I am planning on installing Kodi AC-4 on a laptop (which has NVidia GPU and support for 4K video output) and connecting the laptop as another source into the same entertainment system that currently supports my Shield Tube (with NextPVR as well as NextPVR UI installed) and ATV4K (with NextPVR installed). Since neither the Shield nor ATV4K provides proper full support for AC-4, that means the clients running on those streamers also don't provide full support. I did have some success using uidroid, but I too only got 2.0 audio out instead of 5.1 But I will give it another go.

Anyway, Kodi AC-4 for Windows on the laptop is a terrific alternative solution, that absolutely does provide true working support for AC-4 5.1.  I'm going to get this laptop solution working in the next day or two.

[BrettB]

Anyway, Kodi AC-4 for Windows on the laptop is a terrific alternative solution, that absolutely does provide true working support for AC-4 5.1.  I'm going to get this laptop solution working in the next day or two.

This "terrific alternative solution" is still using ffmpeg to transcode the audio to a different format supported by the client. And it has to do that transcoding every time the file is played.

I would maintain that a better solution would be to do what Martin had been suggesting to you for quite some time now and use an Extra device with NextPVR to do the transcoding once when the recording is made and store the recording with an audio format that is supported by all of your client devices (still in 5.1 format). With this solution, you only have to take the hit for transcoding once and you don't have to have any special client support.

[mvallevand]

You guys should not that not only is AC-4 sound in flux from broadcaster and it is definitely pre-release so it won't be of consistent good quality you might expect. Also note this quote for nickk at SiliconDust "My understanding is that the ffmpeg AC4 code will decode 5.1 but it is missing audio-object support and doesn't decode the high frequency content so you don't get anything above 12kHz."

Effectively your ATSC 3.0 broadcasts will have lower audio quality than ATSC 1.0 delivers unless you use the Silicon Dust APP or an Android player with AC-4 codecs. Of course no broadcasts offer better then AC-3 5:1 anyway so you are just living through growing pains of new tech. If I had ATSC 3.0 in Canada with all the issues, I'd just watch and record ATSC 1.0.

Martin

[DSperber]

I would maintain that a better solution would be to do what Martin had been suggesting to you for quite some time now and use an Extra device with NextPVR to do the transcoding once when the recording is made and store the recording with an audio format that is supported by all of your client devices (still in 5.1 format). With this solution, you only have to take the hit for transcoding once and you don't have to have any special client support.

I am willing to do this. But I know nothing. I am just a "competent rookie user" and not a developer. I need instructions (yes, maybe even step-by-step details and possibly screenshots as well) and hopefully an example of exact or similar implementation. I will succeed, but I need sufficient guidance and a push in the proper "written instructions" direction.

Just telling me what the end optimal objective is not enough to let me accomplish it. Please point me to one or more documents, Wiki pages, or forum posts or threads that I can refer to and that will get me started correctly.

Thank you.

[DSperber]

Also note this quote for nickk at SiliconDust "My understanding is that the ffmpeg AC4 code will decode 5.1 but it is missing audio-object support and doesn't decode the high frequency content so you don't get anything above 12kHz."

I was not aware of the <12kHz deficiency in its AC4 code in this early version of Windows FFMPEG. I don't know if this was because of a huge additional programming effort to support higher frequency treble or what, so it's certainly a shame. At least for now.

Depends on the program content of course, how noticeable this will be, and how "deficient" sounding the output will be. Perhaps most audio is <12kHz so the loss is not that terrible. But based on how very good Kodi AC-4 sounds playing ATSC 3.0 channels (especially compared to how poorly the HDHR app with cloud-assisted faux-5.1 decoding sound) I'm definitely fine with it for now.  It may not be fabulous and theater-quality, but it's very good. And watching native 1080p video is a real plus especially on FOX-carried sports events. Yes, ATSC 3.0 is work-in-progress, so this is all just fun right now.

Effectively your ATSC 3.0 broadcasts will have lower audio quality than ATSC 1.0 delivers unless you use the Silicon Dust APP

I feel that the audio quality provided by the HDHR app (which uses real time continuous cloud-assisted AC-4 decoding when watching an ATSC 3.0 program) is very poor. It is not truly the underlying 5.1 input audio. It is a fabricated and up-mixed faux 5.1 that occupies 5.1 channels but derived from 2-channel stereo.

I think it's like the AC-4 decoding that's built into LG OLED TV's since 2017, which puts out down-mixed 2.0 stereo when playing AC-4 5.1 audio, intended for playback on the TV speakers. And if you reconfigure audio to send it out via ARC/eARC, it is delivered as 5.1 structure but with only 2 channels (L and R) actually populated. I think Silicon Dust is doing the same thing in their cloud-assisted AC-4 decoding, but then turning around and up-mixing that 2.0 to populate all 5.1 channels delivered back down as AC-3 faux-5.1. Looking visually at what they're returning in the C and LS/RS channels is horrifying.  Looks like all five channels (up-mixed to 5.1 from down-mixed 2.0 derived from the original 5.1) are nearly at the same level no matter what the original 5.1 looked like which of course was nothing like this.

Since everything right now is going to be a compromise anyway in the absence of proper AC-4 codecs for all the appropriate platforms, I actually feel the HDHR cloud-assisted result almost sounds the worst. As you say, stick with ATSC 1.0 if you want the best audio.