PCM when speaker configuration is Passthrough

[danieljlevine]

I have a Firestick 4K connected to my Samsung TV and a Dolby Atmos sound bar connected to the TVs eARC port. Things work great for Disney+ Atmos content and I don’t get any complaints from other Dobly Digital Plus 5.1 content apps running on the first stick.

The HDHR app is running on the Firestick 4K as well and has the speaker configuration set to Digital Passthrough. I sometimes see a message saying that Passthrough isn’t supported and that it will use PCM. This is for ATSC 1.0 content served by the HDHR 4K Flex at the moment. Same channel now doesn’t give me the message moments later.

Why does this happen?

[nickk]

It means the app requested AC3 digital passthrough and FireOS rejected the request.

The app will only show the popup once each launch so as not to bug you each channel change.

[danieljlevine]

Ok, so why did it reject the request? And doesn’t that mean SD is handling the AC3 decoding via the cloud?

Is Passthrough the correct setting in my case? Or should I switch it to 5.1 or 7.1 instead? My Atoms sound bar is 5.1.2.

[nickk]

The only codec that may need cloud transcode is AC4 depending on the player device.

In passthrough mode (when working) the AC3 audio is delivered via HDMI and decoded by whatever sound device you are using.

Quick workaround for a 5.1.2 sound bar is to select 5.1 Surround Sound in the app settings menu.

It would be interesting to see if diagnostic logging reports anything... can you please enable "send diagnostic information" in the app settings menu, try passthrough again, then reply back with the Device ID of your HDHomeRun

[signcarver]

Many samsung tvs, particularly older models, fail to handle ac3 passthrough via hdmi. My M series or later never had such issue... k series was hit and miss, and earlier hardly ever worked. In someimes also depends on port used (i had one tv that only accepted such on the same port used for earc).

There is no online transcoding done for ac3... that is for ac4.

[danieljlevine]

10A296FB

Ok diagnostics are on and I tested some channels and now I don’t get the message.

[nickk]

FireOS is reporting AC3 passthrough support however we disabled support on this specific model of FireTV - "Amazon Fire TV 4K (non-max) cannot handle the channel count changing when AC3 passthrough is used - tested 20220318". No other modern FireTV models have this problem.

I will retest today... if Amazon fixed the problem we will enable passthrough.

[danieljlevine]

How did the testing go?

[allen98311]

I also get this message when tuning into a ATSC 3.0 channel, but the AVR says that it is a Dolby surround signal being received.

[Cabal]

I also get this message when tuning into a ATSC 3.0 channel, but the AVR says that it is a Dolby surround signal being received.

Depending on the device, it's probably transcoding into DD/DD+ on the way out. You may be losing channels in the process, it can be tough to debug.

[nickk]

AC3 passthrough channel-count change is working on the Fire TV 4K Stick after installing all Fire OS updates.

Block removed - you should now have passthrough support.

[danieljlevine]

So this does or doesn’t require an app update? It sounds like it was just a change on SD’s cloud side. But I would have thought it to be an app change.

[Cabal]

I infer that the feature whitelist/blacklist is read on start along with the UI configuration.

[jasonl]

Correct, we maintain a separate block list that the Android app checks so that we can add and remove things and have them go into effect immediately instead of needing to wait hours or days for approval.

[danieljlevine]

Can you check my system logs again. I was seeing a different audio message yesterday. I wasn’t able to read it in time but I believe it had “surround sound” in it. I’m assuming when I see an audio message like this things aren’t working perfectly.