[encrypted-media] Allow getStatusForPolicy() to reject the promise with NotSupportedError (#513)

xhwang-chromium has just created a new issue for https://github.com/w3c/encrypted-media:

== Allow getStatusForPolicy() to reject the promise with NotSupportedError ==
The `getStatusForPolicy()` API was proposed as the solution to https://github.com/w3c/encrypted-media/issues/311, to provide a method to early detect the HDCP status.

The current explainer is at https://github.com/WICG/hdcp-detection/blob/main/explainer.md, which states that:

> If HDCP is available at the specified version, the promise should return a MediaKeyStatus of "usable". Otherwise, the promise should return a MediaKeyStatus of "output-restricted"...

> A MediaKeyStatus value of "status-pending" must never be returned. Implementers must give decisive actionable return values for developers to make decisions about what content to fetch.

However, there are platforms where the CDM can enforce HDCP status internally, but there's no easy way (e.g. lack of exposed API) to detect the HDCP status without creating a `MediaKeySession` or obtaining a license. In this case, returning `usable` or `output-restricted` are both wrong and misleading.

After talking with @joeyparrish, we propose to allow `getStatusForPolicy()` to return a rejected promise with `NotSupportedError`, when the CDM might be able to enforce HDCP, but there's no way to detect it in advance. Applications can still use other ways to detect HDCP status, e.g. after obtaining a license.

User agents should strive to return a meaningful status whenever possible. If we know that a certain class of device or a certain version of the OS can't enforce HDCP at all, we should return `output-restricted`.

Please view or discuss this issue at https://github.com/w3c/encrypted-media/issues/513 using your GitHub account


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Received on Monday, 9 October 2023 23:40:42 UTC