I am having an issue where thumbnails for videos are not being generated and the icon is instead just a default video icon. This has been a problem with .mkv and most .mp4 files. It will display some mp4 thumbnails just fine, but others it will seemingly randomly not display. It doesn’t seem to be an issue with the file size as I have for instance, a 50mb video with the thumbnail displayed correctly and a 3.5mb video with the thumbnail not displayed.
I have tried:
going into the preview preferences for Nemo and setting it to always show thumbnails and for files smaller than 32 GB (the maximum i could set it as)
removing the ~/.cache/thumbnails folder
installing ffmpegthumbnailer and ffmpegthumbs
installing nautilus and seeing if it would display thumbnails better which it did not
installing Manjaro XFCE in a VM and placing some of the problematic mp4’s onto the desktop, and the thumbnails were correctly displayed
EDIT In case anyone else is having this issue, I have determined that this is an issue with the thumbnailer that comes with the xplayer media player application that comes pre-installed with Manjaro Cinnamon. Uninstalling it and using a different thumbnailer fixed this.