[Bug 27055] Surfacing license to the user

https://www.w3.org/Bugs/Public/show_bug.cgi?id=27055

--- Comment #20 from Mark Watson <watsonm@netflix.com> ---
(In reply to Sergey Konstantinov from comment #19)
> (In reply to Mark Watson from comment #18)
> > The CDM has no control or visibility of caching or storage of encrypted
> > media performed by the UA or application. The CDM decrypts, decodes and
> > possibly renders the media at playback time.
> 
> Yes, it is. But UA and/or webapp may cache encrypted frames, and they
> should be able to know if CDM rejects those frames.
> 
> > 
> > >     * terms for replaying content;
> > >     * terms for using content offline;
> > 
> > The CDM likely does not generally know whether the device is online or
> > offline (the CDM may not access the network directly for playback-specific
> > operations). So, the primary issue is whether the license is still valid at
> > the time of playback.
> > 
> > We already expose an "expiration" time to the application, but there could
> > be other properties of the license which make it not so useful for offline
> > playback. 
> 
> Another obvious case is a possibility to purge cache via license response.
> I'd prefer this sort of behavior to be somehow formalized.
> 
> > 
> > >     * operations requiring internet connection.
> > 
> > The specification is clear that direct network access by the CDM is
> > restricted to origin-independent initialization (e.g. individualization).
> > 
> 
> Okay, let me say it another way: we need to understand cases when CDM may
> reject
> to render content. One case is license expiration, but there are others.
> For example, in #13 Henry mentioned that seeking backwards needs new license
> to be somehow obtained.

Henri did say that, but I don't think that kind of restriction can be
implemented with EME, at least not reliably.

Timestamps are in the clear in CENC files. If the CDM performs decrypt+decode,
it's not necessary for the CDM to be given the timestamps of the frames in any
form it could understand. If the CDM is given timestamps, there's nothing to
stop the UA ensuing they are monotonic even when the user seeks backwards.

Still, given the variety of ways that the technical license could differ from
the product terms in the online case I still don't see how this can be made
practical and intelligible to users.

I do see that for the particular case of offline playback, things may be more
tractable. For offline, you know that you have got only what you have got in
terms of license permissions. 

It might be interesting to explore ways that the restrictions associated with
licenses intended for offline use could be exposed. One way is through the
(offline version) of the web application, but perhaps there are limits on what
can be done that way ? For example, it might be nice to get a reminder if an
offline license is about to expire.

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Received on Wednesday, 3 December 2014 17:08:06 UTC