cgeffex After messing with this issue for awhile, I found this ffmpeg command to solve the issue in a slightly simpler way (no re-encoding):
ffmpeg -i input.mkv -map 0 -codec copy -bsf:v hevc_metadata=colour_primaries=2,hevc_metadata=transfer_characteristics=2,hevc_metadata=matrix_coefficients=2 output.mkvI tested it on 3 different files that initially had the rec.709 color issue and it fixed them all without re-encoding any audio. After running this command in ffmpeg, Roku/Plex will play the file and transcode the original audio without issues. It's confusing because MediaInfo still shows the BT.709 color flags, but Plex doesn't seem to see them and the files play fine from what I can see. Would love to hear if you're able to re-produce my results.
Maybe you can describe how to do this assuming we know nothing about what you are talking about. Because I have no idea how to try this 'fix' you have come up with but I would like to.
What is an ffmpeg command and how the heck do you paste that to the file?
Does it alter the file so it's changed? Or do you have to keep doing this every time you add the file back to Plex if you remove it?
Emissary35 here's a post explaining how to setup and use ffmpeg: https://video.stackexchange.com/questions/20495/how-do-i-set-up-and-use-ffmpeg-in-windows (assuming you're using windows)
It appears Roku OS 13 has fixed this issue. Can you test and verify?
