[rtcweb] Changing video size (Re: use case:)

[Harald Alvestrand <[e-mail]>]

On 06/17/11 21:38, Aron Rosenberg wrote:
> On Fri, Jun 17, 2011 at 11:09 AM, Cullen Jennings <[e-mail] 
> <mailto:[e-mail]>> wrote:
>
>
>     Video Size Change.
>
>     Alice and Bob are in a video call in their browsers and have
>     negotiate a high resolution video. Bob decides to change the size
>     of the windows his browser is displaying video to a small size.
>      Bob's browser should be able to regenerate the video codec
>     parameters with Alice's browser to change the resolution of video
>     Alice sends to match the smaller size.
>
>
> Changing compression due to a user change in window size is usually 
> not done since it has a bad long term effect on video quality. In 
> almost all the major video calling systems, video resolution is a 
> function of current bandwidth (which changes as the rate control 
> system detects differences) and/or constrained by the physical device, 
> but not a function of a user dragging the window size. At 
> an equivalent bitrate, it is better to compress a larger resolution 
> and display it smaller (higher PSNR), then compress a smaller 
> resolution if you are within the codec's effective bitrate for that 
> larger resolution.
Interesting info, but I don't know if it's true in all cases.

If the overall constraint on a conferencing system is bandwidth, the 
system might find the saving in average bandwidth saving of encoding 
from a base image of 140x200 for "small" windows rather than "HD" 
(720x1024?) worth considering, even though the sending of a complete 
I-frame to reinitialize the video stream might take some effort.

I like having the use case of "change recipient video window size, and 
as a result change sender bandwidth usage"; we might argue about the 
exact phrasing of the use case.

                    Harald