W3C home > Mailing lists > Public > public-webrtc@w3.org > July 2013

Re: setting bandwidth

From: cowwoc <cowwoc@bbs.darktech.org>
Date: Wed, 24 Jul 2013 01:46:35 -0400
Message-ID: <51EF6A3B.8070404@bbs.darktech.org>
To: public-webrtc@w3.org
On 24/07/2013 12:26 AM, Cullen Jennings (fluffy) wrote:
> On Jul 18, 2013, at 6:21 AM, Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com> wrote:
>
>> 2. Setting BW for a MediaStreamTrack
>> ------------------------------------
>> Why: There are situations where a suitable start bit-rate can be known,
>> or guessed. If this knowledge could be used the perceived end-user
>> quality could be improved (since a higher quality is available from
>> start since there is no need to start at a really low bit-rate).
>>
>> There are also situations where it could be beneficial if min and max
>> bit-rates to be used can be influenced.
>>
>> * The app developer may know that below a certain bit-rate the quality
>> is so bad that the browser could stop sending it, and likewise there may
>> be knowledge about a bit-rate above which the quality does not improve.
>>
>> * There are situations when there is an agreement between the service
>> provider and the connectivity provider about min and max bit-rates.
>>
>> What: Again, this depends on how much BW info is included in the SDP.
>> But my understanding is that there should be some (since RTCP rates to
>> be used are based on this info IIUC).
> I agree and think we need to a couple things here. One is setting the limits for the bandwidth but the  other is using the stats interface to read the current bandwidth being used.

     A slightly related but higher-level proposal: replace Mandatory 
constraints with Optional constraints that act as Fence conditions.

     It works like this: You specify a bunch of optional constraints and 
a callback to be invoked when a Constraint is violated. For example, I 
would ask for a bandwidth between 1Mbit and 2Mbit. If bandwidth drops 
below the minimum, the callback gets invoked. I then reduce the video 
resolution, or turn off audio, or... whatever the application wants... 
and set new min/max bandwidth bounds. If the maximum bound is surpassed, 
I know I can afford to increase the video resolution so I do so. And so on.

     Assuming I'm wrong (you need mandatory constraints) I still think 
adding this fence behavior puts control in the right place. The 
application is uniquely positioned to decide what happens when the 
connection capabilities change.

Gili
Received on Wednesday, 24 July 2013 05:47:24 UTC

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