Support videos in Offline Cache

Feature description:

Videos can be included in offline cache

Problem solved:

Right now I can play music videos by navigating to files and playing the music videos manually (at least for my .mkv vids with opus encoded audio), but I cannot include them in offline cache. Tapping on adding to offline cache seems to do nothing as far I can see when I go to manage offline files

Brought benefits:

Videos can be kept in the offline cache and play without internet connection

File mode can’t work offline and there no plans to support videos.