Jellyfin on FireTV transcoding 2.0 FLAC to AAC?

[TheJellyMan]

Last night I tried playing a large remux file from Bluray. All of the audio tracks are in FLAC, yet for some reason Jellyfin was still transcoding. This caused about a frame of severe pixelated distortion every 5 minutes or so, which was super annoying. I checked the logs and the admin dashboard, it looks like Jellyfin was transcoding the FLAC audio to AAC:


Stream mapping:
  Stream #0:0 -> #0:0 (hevc (native) -> hevc (hevc_vaapi))
  Stream #0:1 -> #0:1 (flac (native) -> aac (libfdk_aac))


 Why is that? I thought FLAC was supported. I watched a different remux the other day with mono FLAC audio and didn't notice any issues with playback.

[TheJellyMan]

Update: Last night I watched another large remux file I had with mono FLAC audio and the video glitches happened less but they were still there. I tried using VLC as an external player but then that was causing a different issue where every time the subtitles came up there was a frame skip, so I switched back to the internal Exoplayer. I'd just like to know why these aren't direct playing on LAN. The documentation says I should be able to do it.

[TheJellyMan]

Update: I seem to have partially identified the problem.

The problem was not with audio at all. Audio was only transcoding because I had "Downmix to Stereo" (the default option) checked in the playback settings. Even when playing 2.0 and 1.0 channel audio, it seems that this option still makes the server convert any audio to AAC.

The problem seems to be with Dolby Vision. Although my TV says it supports DoVi, every file that I try to direct play fails, while files with HDR10 pass through just fine. I believe this might be related to the following github issue: https://github.com/jellyfin/jellyfin-and...ssues/4892

I'm still not marking this as solved because I'm not sure what's happening here, but it appears to be a bug in the Jellyfin software.