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?
Confirmed! Sweet, we've been waiting on this fix for AWHILE.
Yes it's confirmed, this annoying playback glitch has finally been fixed! You can now stream HEVC mkv files on Plex on all newer Roku devices and the color saturation problem is gone!
Before these types of files would only display correctly on my older Roku devices or on my Fire TV devices.
It's about time Roku finally did something right and fixed this. But it still took way too long to be addressed, I hope in the future Roku comes up with updates to fix problems like this much faster.
Curious how this fix has worked for other people - the color on my Roku is correct if I transcode, but if I select "force direct stream" for a 4k Dolby Vision source the color is still off. My Plex server is a NAS so can't really keep up with transcoding 4k content, leaving me to direct stream it and have the Roku transcode as my only practical option (with current equipment).
