Audio quiet when transcoding to stereo from 8 channel surround sound

[alchemy]

When I play back a movie through either the browser or jellyfin media player on a desktop with a stereo output and the source audio is 8 channels the result is very, very quiet. 6 channel surround sound seems to be downmixed properly.

I have tried both Dave750 and NightmodeDialogue algorithms with an audio boost of 3.
I have tried setting max allowed audio channels to 2 in both the browser and JMP.

I have tested this across multiple files and found the following:
8 channel TRUEHD: quiet
8 channel DTS-HD HRA: quiet
6 channel DTS-MA: fine
6 channel DTS-HD MA: fine


Thanks for any help!

[TheDreadPirate]

Is the video direct playing or is it transcoding? None of those algorithms apply if it is direct playing the video.

[alchemy]

Ah I misunderstood when downmixing is active then. Yes the video is direct playing. I have seen before transcoding when an audio codec is unsupported but that doesn't seem to be happening even when I have maximum allowed channels set. Is there something I'm missing to get audio to transcode even when video does not need to?

[TheDreadPirate]

The only way to force transcoding is the quality selector. The name is inaccurate. It is more like a "max bit rate" setting. Select a bit rate that is lower than the video's native bit rate and it will force a transcode.

Some clients also have a max audio channels setting that might trigger an audio transcode and downmix.

[alchemy]

Ah yes that's the issue I'm having then. I've set Maximum Allowed Audio Channels in both the normal web ui as well as JMP and this setting does not seem to be respected.

[TheDreadPirate]

Audio transcodes should honor that setting. I'm not sure if direct plays will honor that setting or if Jellyfin just downmixes locally or something.

[alchemy]

I think I may have figured out what's going on

https://github.com/jellyfin/jellyfin/blo...r.cs#L2659

It looks like someone just ripped this stackexchange post:
https://superuser.com/questions/852400/p...ing-ffmpeg

So it seems there is currently no actual downmixing algorithm implemented for 8 channel (7.1) audio.

I'll go ahead and create a ticket for this on the repo.