Re: [rtcweb] Video resolution SHOULDs (Re: resolutions in draft-cbran-rtcweb-codec-01)

["James M. Polk" <[e-mail]>]

At 04:10 AM 11/17/2011, Harald Alvestrand wrote:
>On 11/17/2011 05:54 PM, Stephan Wenger wrote:
>>The highlighted part of Harald's suggestion below
>>
>>    SHOULD support resolutions of 1920x1080, 1280x720, 720x480, 1024x768,
>>
>>       800x600, 640x480, 640 x 360 , 320x240 *if these resolutions 
>> can be displayed on the target device*

I think Harald's suggestion included "Must support 320 x 240" too, 
which is listed as a MUST and SHOULD throughout this thread (which I 
believe is in error). If this resolution is specified, it needs to be 
either MUST or SHOULD, not both.

Roni has a good suggestion about the ability of a receiver to request 
a resolution in SDP, but I think we still should have a given 
resolution defined here, and understanding that each device could 
have wildly different capabilities, Harald's suggestion above covers 
the most cases IMO but only with the text between the * ... * included as well.

James


>>seems sensible.  However, I have another issue.  I don't believe 
>>that naming specific resolutions is advisable.  In a system where 
>>the rendering side has almost undefined picture properties because 
>>they are typically rendered in "windows", it IMO does not make much 
>>sense to limit yourself to certain aspect ratios, picture sizes 
>>etc., even if those correspond to today's preferred sensor 
>>resolutions (or integer fractions thereof).  Resampling an input 
>>signal is cheap nowadays (at least compared to the encoding 
>>itself), and cropping is even cheaper.
>>I would instead recommend naming one single MUST resolution (as the 
>>draft does) to ensure minimum interoperability, and otherwise 
>>negotiate a processing rate in macro blocks per second (or 
>>equivalent), with fixed constraints around the aspect ratio.
>For requirements, I prefer to list specifics, because they're testable.
>
>One of my colleagues had a failing test the other day because he'd 
>specified a picture height of 94 pixels - he did not know that his 
>encoders only supported pixel counts that were multiples of 8.
>
>Of course a device will not fail to interoperate just because it 
>supports decoding more resolutions than those that are required.
>
>BTW, I believe 640x360 is a 16:9 aspect ratio, so handling both 16:9 
>and 4:3 seems to be a SHOULD based on this resolution list. I assume 
>that's intentional.
>
>
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