Replace full-screen background when viewing films

[pilsnerbeer]

Is your feature request related to a problem? Please describe.

white background should be replaced with black for better experience when watching videos.
(See screenshot)

Additional context

Screenshot:
full-screen mode enabled, white croplines visible on top and bottom
(not entirely visible due to white background here on github but you get the idea)

[AndyScherzinger]

@pilsnerbeer what version of the app are you using?

@tobiasKaminsky I only get to see the non full screen version for mp4 and master branch

[pilsnerbeer]

3.12.1 from F-Droid. You must tap the screen in order switch to full-screen mode

[AndyScherzinger]

3.12.1 from F-Droid.

Thanks

You must tap the screen in order switch to full-screen mode

... which is what isn't working for my on the latest master code base

[tobiasKaminsky]

Multimedia buttons also do not work. :-/
Currently I have no clue what happens there…

[tobiasKaminsky]

The PR fixes black background.
Media control is in #7339
Crashing video in #7340