Confused About Transcoding Reason

[doublesteelix]

I have a collection of files which are transcoding, and I do not understand why. They use AV1 for video and AAC LC for audio in an MKV container. Based on the documentation, both the video and audio codec should be supported on Firefox, but the container is not.

I did attempt to look for similar issues, but I did not see anything recent about why it looks like the video is being transcoded when the audio codec is the reason for transcoding (and possibly that this audio codec is also just being copied?)

Expectation:

• Jellyfin will remux the content into a .mp4 container with no transcoding
  
• Failing that, Jellyfin would transcode the audio while copying the video, presenting AV1 to the client
  

What's happening:

• Video is transcoded to H264
  
• Uncertain: It looks like the audio codec is just being copied, despite Jellyfin stating this is the reason for transcoding?
  

Other Notes:

• I was able to direct-play these videos when they were in .mp4 containers. I wanted to add better subtitle support via .MKVs and assumed remuxing would be a minor concern while allowing me to include additional subtitles
  

Jellyfin version:

• Version: 10.8.10
  
• Operating System: Linux
  
• Docker: No
  

I've attached a screenshot with the playback info, showing the transcoding information and original and new codecs. I've also attached the Jellyfin and FFMPEG logs downloaded from the admin dashboard. (I trimmed the Jellyfin log to the last reboot before this. Please also note that I was attempting to force this to remux by disabling video transcoding before re-enabling it for the last entry, at 2023-07-18 05:19:XX).

I would really like to keep .MKVs for their support of many subtitle tracks and am very happy to allow remuxing. I would like to avoid transcoding both for power and video quality reasons.

[TheDreadPirate]

This is typical of watching in a browser. All my content encoded in HEVC, and various audio codecs, always transcodes both audio and video in Chrome. But direct plays when using the desktop Jellyfin Media Player.

[doublesteelix]

Your experience lines up with the linked documentation, unless you add the flag to enable HEVC support. (I believe this is a fairly recent addition to Chrome, which did not support it for a long time.)

I would like to know why a video is being transcoded despite the documentation stating that both the video and audio codecs are supported, and looking for help figuring out why it flags the audio codec as not supported, but then copies it with ffmpeg: 

Code:

/usr/lib/jellyfin-ffmpeg/ffmpeg -analyzeduration 200M -ss 00:02:48.000 -f matroska,webm -autorotate 0 -i file:"/media/jellyfin/series/Community/Season 3/Community s03e10 - av1.mkv" -map_metadata -1 -map_chapters -1 -threads 0 -map 0:0 -map 0:1 -map -0:s -codec:v:0 libx264 -preset veryfast -crf 23 -maxrate 3600668 -bufsize 7201336 -x264opts:0 subme=0:me_range=4:rc_lookahead=10:me=dia:no_chroma_me:8x8dct=0:partitions=none -force_key_frames:0 "expr:gte(t,168+n_forced*3)" -sc_threshold:v:0 0 -vf "setparams=color_primaries=bt709:color_trc=bt709:colorspace=bt709,scale=trunc(min(max(iw\,ih*a)\,min(1920\,1080*a))/2)*2:trunc(min(max(iw/a\,ih)\,min(1920/a\,1080))/2)*2,format=yuv420p" -codec:a:0 copy -copyts ...

Note especially:

Code:

-codec:a:0 copy

after flagging this as the reason for transcoding