Prevent loading com.apple.streamingkeydelivery key format

[valotvince]

This PR will...

Prevent trying to load a com.apple.streamingkeydelivery format skd://... and warn the integrator this isn't supported out-of-the-box by hls.js

Why is this Pull Request needed?

I am working on playing HLS fMP4 w/ Fairplay encryption com.apple.fps.2_0 with hls.js and it was creating an error while trying to load skd:// over HTTP.
Preventing it allows segments to be added to Buffer/MediaSource and therefore trigger the webkitneedkey and webkitkeymessage events that I need to get a license from our DRM provider

Are there any points in the code the reviewer needs to double check?

Any other KEYFORMAT should work

Checklist

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• API or design changes are documented in API.md

[robwalch]

@valotvince thanks for the contribution. Would you consider contributing a fairplay implementation as well? It would be great if we could handle webkitneedkey and webkitkeymessage via the eme-controller or a fairplay variant of that controller specifically for the webkit prefixed API.

[valotvince]

@robwalch Hello :)
I am still developing that feature (out of hls.js) but I'll contribute as soon as I have something working on my end !

[springuper]

@valotvince look forward to your contribution for FairPlay support!