[Bug 25092] Need a way to inform script that resolution restrictions are applied

https://www.w3.org/Bugs/Public/show_bug.cgi?id=25092

--- Comment #16 from David Dorwin <ddorwin@google.com> ---
(In reply to Mark Watson from comment #15)
> Ok, let me check I understand how this would work:
> 
> The license would contain the key and its true key ID, matching the key ID
> in the content files. The license would also contain policy for resolution
> restrictions and one or more 'fake' key IDs corresponding to different
> resolution levels. The client side of the app knows these fake Key IDs
> correspond to resolution levels.

They really correspond to policies, which the application may further map to
resolution levels.

> The new API would expose the key IDs, both the fake ones and the real one
> (or possibly just the fake ones ?).

All key IDs would be exposed - the CDM doesn't know about fake key IDs. In the
downscaling case, the real key ID would always be "usable".

> The CDM would signal changes in
> resolution restrictions as changes in the usable key IDs.

Yes, The CDM would indicate whether the whether all of the reasons to restrict
resolution are false (fake key ID is listed as usable) or not (fake key ID not
listed as usable)

> Did I get this right ?
> 
> Seems like a real kludge where the key IDs are being abused to represent
> different policies that may or may not be applied. The fake Key Id is really
> a 'policy identifier' and the 'usablekeyschange' is being abused to indicate
> a policy change.

In the single key ID case, it is. This is really a case of using a general
purpose API (bug 25409) for a specific use case.

EME relies on and exposes a few basic concepts, including sessions and key IDs.
It doesn't expose policies, robustness, resolutions, etc. Even if we wanted to
expose those, it would be difficult to get consistent definitions/behavior. A
fake key ID seemed like the best way to use the existing common primitives to
address this specific use case.

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Received on Tuesday, 29 April 2014 00:16:22 UTC