Re: EME-protected VIDEO element and drawImage

On Wed, Jan 15, 2014 at 4:25 AM, Hans Schmucker <hansschmucker@gmail.com>wrote:

> There is a slight issue wit EME protected and Canvas, since EME-protected
> content may not be drawable, because it is protected.
>
> There are already provisions in the Canvas2DContext specification which
> are already nearly able to deal with this issue, but they're a little to
> narrowly defined.
>
> Specifically:
>
> http://www.w3.org/TR/2dcontext/#dom-context-2d-drawimage :
> "If the image argument is an HTMLImageElement object that is not fully
> decodable, or if the image argument is an HTMLVideoElement object whose
> readyState attribute is either HAVE_NOTHING or HAVE_METADATA, then the
> implementation must return without drawing anything."
>
> EME does not affect the readyState, but it may not be fully decodable.
> Problem is, that condition only applies to HTMLImageElement.
>

How is it not decodable?
>From the spec:

When an img<http://www.whatwg.org/specs/web-apps/current-work/multipage/embedded-content-1.html#the-img-element>
element
is in the completely
available<http://www.whatwg.org/specs/web-apps/current-work/multipage/embedded-content-1.html#img-all>
 state *and* the user agent can decode the media data without errors, then
the img<http://www.whatwg.org/specs/web-apps/current-work/multipage/embedded-content-1.html#the-img-element>
element
is said to be fully decodable.


Since the user agent can decode the encrypted video stream, this property
doesn't apply.

I would suggest we change it, so that it applies to HTMLVideoElement as
> well:
>
> "If the image argument is an HTMLImageElement or HTMLVideoElement object
> that is not fully decodable, or if the image argument is an
> HTMLVideoElement object whose readyState attribute is either HAVE_NOTHINGor
> HAVE_METADATA, then the implementation must return without drawing
> anything."
>
> Does anybody see any issues with that?
>

The text for  "fully decodable" is only for images.
I believe you should request to update the <video> tag [1] so it can flag
the protected state. The canvas spec can then refer to that flag.
Is there a reason why this flag would disallow drawing? It seems that
setting the *origin-clean* flag to false is sufficient.

1:
http://www.whatwg.org/specs/web-apps/current-work/multipage/the-video-element.html#the-video-element