Add support for switching codecs

[avelad]

Switching codecs are to begin experimentation via origin trials in Chrome 70.

https://www.chromestatus.com/features/5719220952236032
https://bugs.chromium.org/p/chromium/issues/detail?id=605134

Is it possible add support for it in a future release?

Caniuse: https://caniuse.com/mdn-api_sourcebuffer_changetype

[theodab]

Yeah, we want to add this eventually. Hopefully by the time that Chrome 70 is out, if possible.

[avelad]

More Info:
https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/A5Ux5CzpeWs/KjIcVDmpDAAJ
https://rawgit.com/wicg/media-source/codec-switching/index.html

[avelad]

Added in webkit: https://bugs.webkit.org/show_bug.cgi?id=188626

Added in Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=1481166

[avelad]

Added in Safari Technology Preview release 64: https://developer.apple.com/safari/technology-preview/release-notes/

[avelad]

More info: https://developers.google.com/web/updates/2018/09/chrome-70-media-updates

Sample: https://googlechrome.github.io/samples/media/sourcebuffer-changetype.html

[joeyparrish]

This hasn't been updated in a while, so it's worth pointing out some changes to this plan.

As originally proposed, switching codecs was either implemented or not. Now, support depends on the decoding pipeline, and we can only query that with MediaCapabilities. Our MediaCapabilities integration is well underway.

[FireMasterK]

w3c/media-source#155 seamless codec switching should be possible too, since this is merged

[avelad]

I began to look at this functionality and I have doubts, you have to call SourceBuffer.changeType to change the MSE codec/container, but what would happen as EME, would you have to restart EME? @joeyparrish, you have much more control of this part, you can help me.
If the EME needs to be reset, I think we should first address: #1567

[joeyparrish]

@avelad, sorry I didn't see your comment sooner.

I don't believe EME necessarily needs to be reset, but EME may add a layer of restriction to what transitions are possible with changeType. In context of decodingInfo() results that include EME, we would then ask MCap which transitions are supported among the supported codecs. That may be the entire set of supported containers/codecs, or it may be a subset. The logic for how to handle subsets has yet to be designed. And that logic needs to be designed and implemented even for clear content, because the API does not guarantee that you can switch between all supported codecs. (Though I expect that to be the case for evergreen desktop and mobile browsers.)

[dsparacio]

This has become a big topic recently at paramount. We are ready to help implementing this based on the designs and approaches discussed. Supporting both sides of Chrome 70 is interesting. Has there been anymore discussion around this as of recent? Is there a bigger ticket around this topic?

[joeyparrish]

No more recent discussion than what you see here, as far as I recall.