media player doesn't play mp4

[MorrisJobke]

media player doesn't work with mp4 format. Android camera produces mp4 format. Owncloud android app uploads file automatically to the owncloud server. But it isn't possible to play the file with the media player.

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Originally reported by @zerginator at owncloud-archive/apps#1083

[jancborchardt]

The »media player« is a Music app and will never be a Video player because that’s a different thing. We need to properly use the name to avoid confusion. @kabum can you please rename every occurence of »media« to »music«?

That includes renaming this repository from »media« to »music« cc @karlitschek