Fix chrome issue with opus webm videos

[Chocobozzz]

On Chromium/Chrome the media could not be loaded with webm videos that have opus audio

[Chocobozzz]

I'm sorry @feross but it seems this patch does not work. I think we should revert it.

Moreover this patch is not sufficient, because we could also have VP9 webm videos etc. I don't really know how to handle these different codecs with unknown videos on Chrome. Maybe we could parse the chunks to fetch the right codecs, or we could try each codec with fallback (try vp8 with opus, if there is an error try vp8 with vorbis etc). But it's clearly not ideal :/

[feross]

@Chocobozzz I suspected that this wouldn't really help. The fundamental problem is that we're assuming we know the codec based on nothing more than the file extension.

I implemented it this way knowing that videosteam is the proper way to to handle most videos, since it properly detects the codec, etc. (But it doesn't support anything but MP4 for now).

All other formats fallback to this guess-and-pray approach based on file extension and naively using MediaSource. All of these formats using this approach don't support seeking, either.

Not sure if there's a easy way to detect the codec that we could try. Maybe @jhiesey has an idea?