W3C home > Mailing lists > Public > public-webrtc@w3.org > August 2011

Re: Clarification on media capture split between WebRTC and DAP

From: Rich Tibbett <richt@opera.com>
Date: Tue, 16 Aug 2011 17:07:22 +0200
Message-ID: <4E4A87AA.4040708@opera.com>
To: Harald Alvestrand <harald@alvestrand.no>
CC: roBman@mob-labs.com, "public-webrtc@w3.org" <public-webrtc@w3.org>
Harald Alvestrand wrote:
> On 08/16/11 12:10, Rob Manson wrote:
>> +1 for finer grained separate authorisation between streaming to a
>> remote server vs. streaming into a<video> or<audio> tag. This is
>> essential.
> -1.
> I have problems with this - it seems to say that when asking for a
> camera, the JS has to specify API parameters that specify what the
> purpose of the stream is - with an as-yet undefined vocabulary.

1. Always provide a tainted Stream object to a camera-requesting web 
page requiring no up-front user authorization. Treat this Stream object 
as a cross-origin resource, thereby tainting any resulting <canvas> copy 
and disabling all camera snapshot and camcorder recording functionality 
against that Stream object in its tainted state.

2. Require the web app to assign and display the tainted Stream object 
in a <video> element in order for the user to authorize its allowed 
capabilities (in Step 4 below).

3. Let the web app to provide a hint to the Stream object (or <video> 
element) for the type of access to the camera it actually requires - a 
list of one or more of the following tokens: 'camera', 'camcorder', 
'streaming', 'telephony'.

4. Let the UA present the following <video>-overlaid stream control 
buttons to the user depending on the access hint(s) registered above:

   - a 'camera' button > to take a still image capture to generate an 
image file that the web app can register a callback to receive.
   - a 'camcorder' button > to take a video capture to generate a video 
file that the web app can register a callback to receive.
   - a 'streaming' button > to allow the current web page to un-taint 
the Stream object and allow the web app to access that streaming data 
(e.g. via a <canvas> element or an Audio API). Either ON or OFF (default).
   - a 'telephony' button > to allow the current web page to then assign 
the Stream object to the P2P communication API without throwing e.g. a 
Security Violation error. Either ON or OFF (default).

5. On user click of any of the stream control buttons presented, enable 
the inferred functionality, fire a callback to the web app and let it 
continue about it's intended business.

This approach immediately lets the user see that the page is ready to do 
something with their camera without requiring an up-front prompt/access 
authorization. It lets the user get comfortable with the fact that the 
camera is on rather than it happening all at once. It lets them adjust 
their hair before they go live. It presents UA-controlled buttons within 
a <video> element for the user to authorize (or not) the requested, 
targeted usage when they are ready.

FWIW, this discussion is entirely orthogonal to the P2P aspects 
('streaming' in this email refers to streaming the video to the web 
page, or, untainting the provided Stream object. 'telephony' refers to 
the p2p communication stuff).

I can understand the push-back but I'd be interested for webrtc to 
explore such an approach a little further. Accessing the camera without 
streaming the results to a remote server has wide-applicability e.g. AR 
guides, bar-code scanning web apps, camera/snapshot/fx web apps, 
on-demand a/v recording uploads, personal introductions, etc.

- Rich
Received on Tuesday, 16 August 2011 15:07:58 UTC

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