[Delta] Codec negotiation

[Pau Garcia i Quiles]

Quoting Justin Karneges <justin-psi2 at affinix.com>:

> On Thursday 06 November 2008 16:35:09 Pau Garcia i Quiles wrote:
>> 1. Take the resolutions Alice supports (A1, A2, A3) and the
>> resolutions Bob supports (B1, B2)
>>
>> 2. Calculate a very simple "cross-correlation" between each pair of
>> resolutions: A1 and B1, A1 and B2, A2 and B1, A2 and B2, and so on.
>> The "cross-correlation" algorithm could be as simple as the percentual
>> deviation:
>>
>>   0.5 * ( B1_x / A1_x + B1_y / A1_y ) = 0.5 * 1.742 = 0.871
>>   0.5 * ( B2_x / A1_x + B2_y / A1_y ) = 0.5 * 3.484 = 1.742
>>   0.5 * ( B3_x / A1_x + B3_y / A1_y ) = 0.5 * 6.969 = 3.485
>>   0.5 * ( B1_x / A2_x + B1_y / A2_y ) = 0.5 * 0.87 = 0.43
>>   0.5 * ( B2_x / A2_x + B2_y / A2_y ) = 0.5 * 1.742 = 0.871
>>   0.5 * ( B3_x / A2_x + B3_y / A2_y ) = 0.5 * 3.532 = 1.766
>>
>> 3. Take the value closer to 1, i. e. the resolutions which are closer
>> in size.
>
> Yes, this is an interesting approach. :)

:-)

>> In this case, both 160x120 for Alice and 176x144 for Bob, and
>> 320x240 for Alice and 352x288 for Bob would be equally preferred and
>> deciding between those two would be a case of "I prefer a bigger
>> camera window" or "I prefer a smaller camera window".
>
> I'm not quite sure what you mean here.  By "deciding between those   
> two" do you
> mean deciding between the two "sets" { 160x120, 176x144 } and { 320x240,
> 352x288 } ?

Yes

> Also, are you suggesting that "320x240 for Alice and 352x288 for Bob" should
> mean both parties operate at different, but similar, resolutions?

Yes, exactly

> Since
> Alice did not offer 352x288, it is an unusable mode I think.  At least, this
> is the case in Jingle.

Does Jingle require that both participants use the same camera  
resolution? That does not make sense to me!

Why should we "steal" resolution from Bob (32x48 pixels "stolen") just  
to make sure both Bob and Alice see a 320x240 window. Bob or Alice may  
very well then resize the video window (i. e. tell the client  
application to upscale), or have different screen resolutions or  
different monitor sizes, so they no longer see the video window the  
same size (in inches, I mean) even though both of them are capturing  
at the same resolution. For instance: Bob is using a screen resolution  
of 1024x768 (so 320x240 is about 1/3 of his screen) and Alice is using  
a screen resolution of 1600x1200 (so 320x240 is 1/5 of her screen). If  
we don't "steal" those 32x48 pixels Bob. Granted, 352x288 is  
capturing, Alice would see a 352x288 window, which is not much bigger  
than 320x240 but at least it's a bit better.

-- 
Pau Garcia i Quiles
http://www.elpauer.org
(Due to my workload, I may need 10 days to answer)