W3C home > Mailing lists > Public > public-html@w3.org > March 2012

Signaling and out of band content, was: Re: Encrypted Media proposal: Summary of the discussion so far

From: Charles Pritchard <chuck@jumis.com>
Date: Sun, 04 Mar 2012 11:03:09 -0800
Message-ID: <4F53BC6D.1070804@jumis.com>
To: Andreas Kuckartz <A.Kuckartz@ping.de>
CC: Christian Kaiser <kaiserc@google.com>, "<public-html@w3.org>" <public-html@w3.org>
On 3/4/2012 12:41 AM, Andreas Kuckartz wrote:
> On 04.03.2012 02:54, Christian Kaiser wrote:
>> To illustrate, let's assume
>> - browser/device B1 supports CDMs A and B,
>> - browser/device B2 supports CDM A,
>> - browser/device B3 supports CDMs C and D
>> and
>> - content distributor CD1 supports CDM A and C
>> - content distributor CD2 supports CDM A, B and D
>> In this example, *all* browsers/devices can play content
>> from *all* content distributors even though none of the
>> content distributors support all CDMs, and the
>> browsers/devices do not support a common set of CDMs.
> It is noteworthy that this scenario does not include *any* browser which
> does not support *any* of these CDMs but still makes a statement about
> *all" browsers. This scenario is only thinkable in a world in which Open
> Source has been eliminated. Wishful thinking?

Back to some wishful thinking: Is there a means of generalizing this 
proposal? As someone on the list pointed out, this proposal works to 
send out of band data to be processed by the video system. Seems like 
that kind of functionality could be helpful.

One tactic of the Hixie is to unify what are seemingly separate use 
cases into one more-elegant system.

Where this proposal tries to jam key systems into the media framework:
   DOMString canPlayType(in DOMString type, in DOMstring? keySystem);
We could generalize:
   DOMString canPlayType(in DOMString type, in DOMstring? signalSystem);

The authors of the Encrypted Media proposal may find some good feedback 
from WebRTC peoples:
https://sites.google.com/site/webrtc/running-the-demos
http://dev.w3.org/2011/webrtc/editor/webrtc.html

While WebRTC has very different mechanisms and goals, the goals of 
streaming media and signaling are shared.

These are not the same as the Encrypted Media addKey system, but I urge 
the editors to review them anyway:
http://dev.w3.org/2011/webrtc/editor/webrtc.html#widl-PeerConnection-processSignalingMessage-void-DOMString-message
http://dev.w3.org/2011/webrtc/editor/webrtc.html#the-data-stream

While the industry and editors can just move ahead with key-specific 
extensions to HTML Media, they may find less push-back with a more 
broadly applicable proposal. Out of band signaling seems like a concept 
that may have long term uses outside of DRM.

By and large, replace "key" with "signal".

For a simple use case, consider a video stream that is accompanied by a 
drawing overlay, such as used on the TV with sports replays.
It may be helpful to pump in an Array Buffer of x/y offsets (from the 
announcer) as well as timing information, so that the <video> 
synthesizes with an overlay.


-Charles
Received on Sunday, 4 March 2012 19:03:34 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Wednesday, 9 May 2012 00:17:46 GMT