Add cenc KID attribute to the Descriptor class (#47)

[CASchneider]

Added the cenc KID attribute to the Descriptor class to identify cenc KID in the manifests of DRM encrypted content.

[rlaphoenix]

ns2 is an alternative to cenc. What if we do an or situation here instead of creating a cenc specific kid attribute? There's more than just ns2 and cenc as well, but I'm sort of blanking on remembering any more of them.

However, doing an or situation here could cause a breaking change for any users that solely expect it to be for ns2.

[davemevans]

The namespace can be anything, so no solution like this will cover all cases.

I do prefer having cenc to the random ns2 that's currently supported since I imagine most people will probably use namespace cenc, but the only way to really solve it is to make the parser namespace-aware which is probably unlikely.

It's totally possible for users to added support for elements from different namespaces by redefining classes. Sucks a bit, but keeps the core library cleaner.

[sangwonl]

👍 Thanks

LGTM, but I need to follow up the comments.

[sangwonl]

As far as I survey KIDs such like ns2:default_KID and cenc:default_KID belong to ContentProtection tag, right? If so, we'd better insert them to the specific tag rather than extending Descriptor broad.

But, if not, it would be appreciated if you share an MPD example for it.

[sangwonl]

Thanks @CASchneider for your contribution. But I believe that ContentProtection from #54 addresses this cenc attribute in general way. So I will close this PR for now. Thanks.