Support for mkv

[Farzat07]

I see that multiple audio formats are supported, but only mp4 is supported for video.

Is there a reason why other formats such as mkv can't be supported? Codec can't be the problem as when mkv is remuxed to mp4 it works normally, but maybe the container itself is incompatible?

Anyway, if supporting other formats is possible, I am willing to implement it as I know Python, but it would be nice if I could get some guidance in the process.

[Farzat07]

Ok I checked and it seems that mutagen is used as the backbone and it doesn't support mkv so I went on and opened an issue there quodlibet/mutagen#575.