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Re: A Big Proposal: A way to control quality/resolution/framreate/simulcast/layering with RtpSender

From: Chris Wendt <chris-w3c@chriswendt.net>
Date: Thu, 20 Feb 2014 08:18:06 -0500
Cc: Martin Thomson <martin.thomson@gmail.com>, Peter Thatcher <pthatcher@google.com>, "public-orca@w3.org" <public-orca@w3.org>
Message-Id: <A9FB41A0-77C5-428A-8AE2-CF9B6FCF86DE@chriswendt.net>
To: Justin Uberti <juberti@google.com>
I also want to re-iterate the idea that targetQuality represents a slider between 0.0 and 1.0 where 0 is try to allocate as many bits toward picture quality and 1.0 is try to push out as many frames per second, based on input framerate as max, as possible, no matter what happens to picture quality.  0.5 would be the even tradeoff between quality and framerate.
For this, I think you no longer need a bias, and maybe this is similar to what Martin was suggesting before.

Also, bringing audio codecs in the mix, the 0-1 scale for quality may map to preferring higher sampling frequency vs. encoding quality at lower sampling frequency.


On Feb 20, 2014, at 8:03 AM, Chris Wendt <chris-w3c@chriswendt.net> wrote:

> Could also have something like target bitrate and target quality with optional min and max bitrate and quality as a callback to application layer.
> 
> 
> On Feb 20, 2014, at 2:26 AM, Justin Uberti <juberti@google.com> wrote:
> 
>> For min, you can shut off the stream where there aren't enough bits, but what should you do when the stream goes over the application-defined max?
>> 
>> I am very open to having the app do much of this stuff dynamically, since it means the static configuration controls can be simpler, but I'm not sure we can toss maxBitrate/maxQuality.
>> 
>> 
>> On Wed, Feb 19, 2014 at 8:32 PM, Chris Wendt <chris-w3c@chriswendt.net> wrote:
>> 
>> Maybe Iím reading more into this or maybe Iím making it more complex than necessary, or maybe iím stating the obvious, but I think this makes sense.
>> 
>> My originally assumed premise was that you setup a stream with a set of parameters and let the implementation map those parameters to video encoder rate controls and it runs happily along independently doing adaptive bitrate things within the context of the given parameters.
>> 
>> Taking things to the next level, we can imagine having and likely requiring application level control, particularly for SVC and simulcast or in cases where you have multiple RTPSenders, where we need to control across multiple potentially unrelated and independent media streams and based on some metrics feedback that, for example, quality is suffering given some bitrate constraints, so I should switch to half resolution, or no longer send the 3rd enhancement layer or reduce the number of RTPSenders.
>> 
>> So what would be the feedback mechanism here?  Is this up to the application developer to monitor metrics themselves if even possible or practical?
>> 
>> I would propose we think about providing callback hooks based on things like min/max bitrate and min/max quality thresholds.  And maybe specifically define the basic set.
>> 
>> Again, I think the current discussion around the simple set of parameters satisfies the static config case, but when we talk about max or min type of parameters, I think there needs to be some feedback to notify that application when the min/max point is reached so it can act appropriately.
>> 
>> Thoughts?
>> 
>> 
>> 
>> On Feb 19, 2014, at 6:52 PM, Martin Thomson <martin.thomson@gmail.com> wrote:
>> 
>> > On 19 February 2014 15:44, Peter Thatcher <pthatcher@google.com> wrote:
>> >> I think we still need scale for simulcast and maxBitrate for cases where you
>> >> want to constrain bandwidth even when it's available.    And priority vs.
>> >> resources seems pretty similar.
>> >
>> >
>> > I'd like to take simulcast out actually.  I think that aside from some
>> > bindings necessary to get playback right, you can achieve simulcast
>> > transmission (what we are talking about here) by having multiple
>> > tracks with different resolution constraints.  I don't think that
>> > means fewer options sadly.
>> >
>> > Maybe we can also discuss minimums.  I don't think that it's
>> > worthwhile having minimum values initially, and maybe not ever, though
>> > I'm open to the idea.  And I think that it's a universally applicable
>> > thing across all axes.  I can see cases for minimums on all three:
>> > frame rate (sign language), resolution (1x1, my image recognition
>> > can't deal), and quality (my eyes, ow, my eyes).
>> 
>> 
>> 
> 


Received on Thursday, 20 February 2014 13:18:37 UTC

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