[BUG] FireTV app mixing DD and DD+

[humaita]

Server Version#: v1.31.1.6782-77dfff442
Player Version#: 9.17.0.38861 (d37d0eb2)

Hi, I have a brand new Fire TV Stick Lite connected to my TV, and my TV connects through coax to my digital receiver. My digital receiver only supports “Dolby Digital”, it does not support “Dolby Digital Plus”. My Plex App is set to passthrough with DTS and AC3.

Case 1: When I set my Fire TV Stick to passthrough with “Dolby Digital”, then Plex will do a direct play for videos with AAC audio, and the video will not play with the message “An error occured while attempting to play this video”.

Case 2: When I set my Fire TV Stick to passthrough with “Dolby Digital Plus”, then Plex will transcode AAC to AC3, and everything will be fine.

Case 1 should transcode to AC3, and Case 2 should give an error, since my digital receiver does not support “Dolby Digital Plus”. Setting my Fire TV “Dolby Digital Plus” is an issue, as other apps will not have any sound.

Changing Fire TV audio to “Best Available” doesnt help. I also tried changing the Profile Android.xml on the server, but without any luck. Exactly this setup and this server version are working perfectly with my 1st generation Fire TV.

Is this a bug, or any ideas how can this be fixed? Thank you for your support!

[nx6]

Two bits of info missing:

Can you not connect the Fire Stick direct to the receiver? Having HDMI bandwidth to pass the audio over would like yield different results.

Also what are you using for your passthrough setting on the app?

[humaita]

Hi, thank you for the reply.

> Can you not connect the Fire Stick direct to the receiver?
Unfortunately no HDMI port, only SPDIF and coax.

> Also what are you using for your passthrough setting on the app?
My Plex App is set to “Audio passthrough” = “Optical” and “Optical Encodings” = DTS and AC3. I also tested all permutations of these options without any success.

[nx6]

What happened when you set the pass-through on the Plex app to HDMI? Technically it’s the TV that is doing the coax digital output here, not the device.

[humaita]

Hi, thank you for the reply.

Setting passthrough on the Plex app to HDMI will always result in Stereo sound (for all possible set ups in FireTV), i.e. no 5.1 / digital output.

[nx6]

I think at the least you will need to get client logs of trying to play back the video with AAC where it fails. I would suggest making a sample file too, but this sounds like it will be difficult to test since it might have something to do with the specific make/model of receiver.

[humaita]

Hi, good idea. By client logs you mean the server logs?

I used the following publicly available video as a test (instead of generating one): Download

Attached you can find the log with the snippets for Cases 1 and 2.

Plex_Media_Server.log (84.3 KB)

[nx6]

@humaita

Hi, good idea. By client logs you mean the server logs?

I meant client logs really, but honestly you might need both. I just think client logs are a better place to start for an issue that is not impacting every single client.

Nice with the test video. I don’t have a receiver here, but I kinda want to see if I can reproduce this at all with different passthrough settings. Unlikely I will be able to though.

[nx6]

Setup:
Fire Stick 4K Max
2008 Samsung TV/PC Monitor (supports Dolby Digital, not DTS or DD+)
Plex App is currently 9.19.0.85 beta (because it fixes the cast row pictures)
Normal Settings:
Fire Stick Audio: “Best Available”
Plex App: HDMI Passthrough.

Note: Using a test file that has HE-AAC, instead of the more common LC AAC kinda adds an unknown here, anyway…

I can’t produce any issue with the Fire Stick remaining on “Best Available” setting. If I have the Plex app on Optical/DD pass-through, the server transcodes the HE-AAC to 640 kbps AC3. If I have optical set but all formats turned off the server transcodes to Opus (not sure of the point of that, this Fire Stick can handle HE-AAC natively afaik). It plays back fine either way. I don’t have a surround sound system so I can’t say if it’s actually separating channels, but I’m not missing any channels when its playing back.

Now it gets interesting…

I set the Fire Stick to Dolby Digital Plus, and Plex app to Optical/AC3.
I get no sound, but the server is transcoding to plain AC3, which should be playable. So now, is the Fire Stick trying to send the audio through as the original AC3, or is it adding some information that is making the monitor see it as constant-bitrate EAC3? Any playback device that support EAC3 will be backwards compatible.

I set the Fire Stick to PCM, and Plex app to Optical/AC3.
Now I can’t play back the video.

Seems like the server should be transcoding to Dolby Digital, but not sure what the Fire Stick would do to handle the audio here (I want to say downmix to stereo PCM?).

I set the Fire Stick to PCM, and Plex app to HDMI, the test file direct plays fine.

I got smart at this point and turned my navigation sounds back on, and then set the Fire Stick back to Dolby Digital Plus…
Nothing. I’m not getting any navigation sounds. So I’m going to conclude the “Dolby Digital Plus” setting sends ALL audio to the playback device as DD+ encoded.

Set Fire Stick to Dolby Digital.

• With the Plex app on HDMI passthrough the file direct plays.
• With the Plex app on Optical/AC3 the audio is trasncoded to 640 kbps AC3 and plays.

I read sixones recently state that all the models of Fire Sticks have their own idiosyncrasies.

My recommendation at this time is to leave the Fire Stick’s own audio as Dolby Digital so you know the audio is formatted for your receiver passthrough. The “Best Available” is going to judge based on the TV’s own capabilities. After that we’re looking at something Plex will need to chime in on. The server should be transcoding the audio and is not.

Edit: If you’d like a “control group” file for comparison here’s an original AC3 test file I happen to have: Test AC3 v2.0.avi.zip (1.2 MB)

[humaita]

Hi, here is the client log.

Interestingly, in both cases the transcode URL that is called seems to be the same, and in both cases the server seems to trascode audio to AC3. However, in Case 1 we get a “ERROR_CODE_AUDIO_TRACK_INIT_FAILED”.

Plex_Client_Log.log (113.5 KB)