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

[Harald Alvestrand <[e-mail]>]

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*
>
>
> 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.