Intent to Implement: EME: Query what encryption schemes are supported

[John Rummell]

Contact emails jrum...@chromium.org,joeyp...@chromium.org Spec https://github.com/WICG/encrypted-media-encryption-scheme/blob/master/explainer.md Summary 

Provide applications the ability to query whether a specific encryption scheme is supported by EME. Motivation Some platforms or key systems only support CENC mode, while others only support CBCS mode. Still others are able to support both. These two encryption schemes are incompatible, so applications must be able to make intelligent choices about what content to serve to which user agents. Currently applications “know” what schemes are supported on different platforms by different key systems, and so serve content based on determining what platform they are running on. This addition would make it possible for applications to check for support in a common way and avoid having to determine what platform they are on. It also allows platforms to change the encryption modes supported.

Interoperability risk Firefox: No public signals Edge: Public support (https://discourse.wicg.io/t/proposal-further-work-on-encrypted-media-extensions/2623/2) Safari: Public support (https://discourse.wicg.io/t/proposal-further-work-on-encrypted-media-extensions/2623/5) Web developers: Positive (https://discourse.wicg.io/t/proposal-further-work-on-encrypted-media-extensions/2623) Compatibility risk Compatibility risk is low. From the spec: “Applications which don't use the new field will not be affected. If they make assumptions about the capabilities of certain platforms or key systems, they can continue to use those assumptions, with no additional risk. User agents which don't recognize the new field will ignore it. Applications which are aware of the new fields may still need to hard-code assumptions about the encryption schemes supported by these older user agents.” Ongoing technical constraints None. Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)? Yes or no. Yes, except for Android WebView. OWP launch tracking bug http://crbug.com/838416 Link to entry on the Chrome Platform Status https://www.chromestatus.com/features/5184416120832000 Requesting approval to ship? No.

[Rick Byers]

Sounds great to me!  Major sites relying on a UA check to infer support for different features has proven a serious barrier to interop in other contexts, so in general we work pretty hard to try to ensure all Chrome features are reasonably feature-detectable.

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[Ian Kilpatrick]

Horray!

As per: https://docs.google.com/document/d/1vlTlsQKThwaX0-lj_iZbVTzyqY7LioqERU8DK3u3XjI/edit#bookmark=kix.p5nalpch13qw

Please file a TAG review or comment on why the tag review process is being skipped.

Thanks,

Ian

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[Xiaohan Wang (王消寒)]

TAG review requested at https://github.com/w3ctag/design-reviews/issues/322

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