Video sizing on the public share page

[jancborchardt]

When sharing a video via link, the size of the video container should be the same as the video, or maximally the width of the viewport. Currently it looks like this:

(Whereas the actual video is a lot bigger.)

cc @oparoz @Instagit @schiessle

[icewind1991]

No way around this really since we don't know the video size until we start playing

[jancborchardt]

Maybe then we should up the default size to something more reasonable or bigger? What’s a good default? Maybe 1280*720, or maximum the width of the viewport? cc @MorrisJobke

[jancborchardt]

Youtube default seems to be 854*480px, we could go for that.

[jancborchardt]

Fix at #625