W3C home > Mailing lists > Public > public-html-media@w3.org > January 2014

Re: EME: Rendering behavior undefined

From: Mark Watson <watsonm@netflix.com>
Date: Mon, 13 Jan 2014 08:26:37 -0800
Message-ID: <CAEnTvdA458gkKA_=AKWXAGvavnnQY3c+80jKe1OfaVXkc5b2gw@mail.gmail.com>
To: Hans Schmucker <hansschmucker@gmail.com>
Cc: Henri Sivonen <hsivonen@hsivonen.fi>, Philip Jägenstedt <philipj@opera.com>, "public-html-media@w3.org" <public-html-media@w3.org>

Could you say exactly which paragraphs you think should be removed ? (sorry
if you already said that below)

Unless we say anything to the contrary, all the requirements of the HTML
Media Element apply, including all the rendering requirements, compositing
with other content etc. The possibility that the decoded frames may not be
returned to the browser is not intended to change that. For that case,
unless we say differently, the browser would need sufficient control of
what happens to the frames to implement the standard Media Element behavior
without actually seeing the bytes of the decoded frames.

It is likely that the APIs that make decoded content available to
Javascript are incompatible with the robustness requirements of some CDMs,
so it's likely that these specific APIs won't work and we should say
something about that.

It is also possible that the case I describe above - where the browser does
not see the decoded bytes but has sufficient control of how they are
rendered / composited runs into implementation issues. I would expect to
learn about such issues during the implementation phase. Right now, as the
text stands, an implementation which didn't implement the correct
behaviours would not be "interoperable" with one that did. At that point,
we have to decide whether and how to allow such behavious. But I think it's
premature to start discussing constraints now in advance of implementation
experience (and specifically, when there are no implementors yet saying
that they can't implement it without constraints).


On Mon, Jan 13, 2014 at 7:08 AM, Hans Schmucker <hansschmucker@gmail.com>wrote:

> I came here under the same impressions that the authors of these bugs were
> under:
> That it would not be realistic to expect anything but totally opaque
> behavior from CDM vendors. But as you said, that didn't happen. We know
> now, that CDM vendors WILL and DID accept some level of integration.
> The problem is that we're running around in circles here:
> The paragraphs as they stand now go beyond mere decoding... they deal with
> rendering and integration, so naturally any discussion about them will go
> beyond what EME should deal with.
> So, the best way forward might be to remove those paragraphs from EME in
> order to make it into a real decoding-only spec again and move the issues
> over to the media spec where they belong. There we can discuss how
> protected content in general should be treated (not just EME-protected
> content).
> --hans
> On Mon, Jan 13, 2014 at 3:51 PM, Henri Sivonen <hsivonen@hsivonen.fi>wrote:
>> On Mon, Jan 13, 2014 at 2:45 PM, Philip Jägenstedt <philipj@opera.com>
>> wrote:
>> > On Mon, Jan 13, 2014 at 6:32 PM, Hans Schmucker <
>> hansschmucker@gmail.com> wrote:
>> >> In summary, they should be removed and at best be replaced with a note
>> >> saying that usage of a CDM does not change the behavior of the video
>> element
>> >> in any way. Correct?
>> >
>> > Probably not entirely correct, since a video element can normally have
>> > its pixels drawn to a canvas and its audio samples fed into the Web
>> > Audio API. I haven't checked, but I'd be surprised if either of these
>> > are possible using EME...
>> The current spec text on that topic was added in response to
>> https://www.w3.org/Bugs/Public/show_bug.cgi?id=21155 . It seems that
>> the position of the spec is that the interaction with canvas, the Web
>> Audio API and the like depends on the Robustness & Compliance
>> provisions each CDM is subject to instead of depending on EME itself.
>> --
>> Henri Sivonen
>> hsivonen@hsivonen.fi
>> https://hsivonen.fi/
Received on Monday, 13 January 2014 16:27:05 UTC

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