Audio Transcode switches off HDR playback

[dthree]

I get why it needs to transcode the audio for 7.1, and I can confirm it does this with AAC 7.1 files as well as OPUS 7.1 audio. The issue is that it should still direct play the video (Direct Stream as it's called in the docs) while transcoding just the audio, but it's not. When playing Dolby TruHD 7.1 files, the player correctly transcodes the audio to 5.1, and passes through the video, retaining the HDR. Here's an example of that.

Code:

[2024-08-29 15:20:08.082 -04:00] [INF] [49] MediaBrowser.MediaEncoding.Transcoding.TranscodeManager: "/usr/lib/jellyfin-ffmpeg/ffmpeg" "-analyzeduration 200M -probesize 1G -readrate 10 -fflags +genpts  -i file:\"/mnt/Movies/TrueHD_movie.mkv\" -map_metadata -1 -map_chapters -1 -threads 0 -map 0:0 -map 0:1 -map -0:s -codec:v:0 copy -tag:v:0 hvc1 -bsf:v hevc_mp4toannexb -start_at_zero -codec:a:0 libfdk_aac -ac 6 -ab 640000 -copyts -avoid_negative_ts disabled -max_muxing_queue_size 2048 -f hls -max_delay 5000000 -hls_time 6 -hls_segment_type mpegts -start_number 0 -hls_segment_filename \"/cache/transcodes/6fd59b8ffbe8b93c5cf1996370358599%d.ts\" -hls_playlist_type vod -hls_list_size 0 -y \"/cache/transcodes/6fd59b8ffbe8b93c5cf1996370358599.m3u8\""

You can see it's copying the video track and transcoding the audio track to aac 6 channel. I'm not sure why this isn't the behavior for OPUS or AAC 7.1 audio tracks.