I cannot set default association of mp4 and avi files to my custom desktop files. For mkv, I can change from nautilus file>properties>open with tab. This is a video of the peculiar behavior that I am observing. It is hard to describe in words. Every time I click on my custom app in the 'open with' tab of file>properties in nautilus, and click on set as default, it reverts back.

This question has all the particular details of my specific case, but this seems to be a general problem as it is only for some file types . I need to associate all video files to my custom .desktop file. Please help.

I have tried:

Changing the memetypes.list file. Changing defaults.list file Installed Thunar and tried setting association from there

All the attempts had the exact same results.

This might have something to do with the bug mentioned here