I have a set of mkv files generated by MakeMKV, the same as everything else on this server. For some reason, this specific set of files won’t generate thumbnails. Every scheduled task window, the server attempts to generate them but fails with no error.
Files added prior to these successfully generated thumbnails and files added since these successfully generated thumbnails.
I’ve done the Plex dance in addition to emptying the trash, optimizing the db, and cleaning bundles.
Plex also generates preplay thumbnails for the files itself and displays those if there are no online metadata resources for them. Did you check if they were being generated (they will appear in the available options when you edit a single episode)?
If they are also messed up that will point to an issue with your video. In my example the video is 4:4:4 color space. Plex can’t get video frames for this for the episode images, but the video will play back (transcoded on almost all clients).
If you have episode thumbnails generated by the files but not for when skipping around this might be from the number of keyframes in the video encoding or a problem in Plex besides this.
In any case, I think you’re gonna have to supply a sample for Plex to analyze.
If you wanted to show evidence this is a recent change taking a series you have the thumbnails for now and wiping it from your system (clearing bundles, etc), then readding the exact same files to have it not generate the thumbnails it was able to get before is one way. Also server logs to go with the series being processed and not generating them.
So far no one at Plex has responded, so kind of hard to provide them with any samples. And even with verbose on, the logs don’t show any errors. The transcoder exits with a success code but apparently doesn’t produce any thumbnails.
DEBUG - [Req#b793/Transcode/bif/f5123c93-3443-4ea1-824e-7c89563b5afa] Activity: updated activity f5123c93-3443-4ea1-824e-7c89563b5afa - completed 0.0% - Generating video preview thumbnails
DEBUG - Jobs: '/usr/local/share/plexmediaserver/Plex Transcoder' exit code for process 42384 is 0 (success)
ERROR - BaseIndexFrameFileManager: expected 701 images, but found 0
DEBUG - Updating part with ID=47569 [/anime/Neon Genesis Evangelion/Season 1/Neon Genesis Evangelion - S01E09 - Both of You, Dance Like You Want to Win!.mkv]
DEBUG - Activity: Ended activity f5123c93-3443-4ea1-824e-7c89563b5afa.