Re: Proposal: align video scaling with JSEP

Makes sense to me.

On Tue, Sep 26, 2017 at 4:56 AM, Stefan Håkansson LK <
stefan.lk.hakansson@ericsson.com> wrote:

> All,
>
> sorry for a long message, but I've been looking at how to resolve Issue
> #1283 [a] 'centering, scaling, cropping'. The Issue itself says that
> JSEP and webrtc-pc are not aligned and was reported by Ekr as part of
> his full read through of webrtc-pc in May.
>
> Long story short: I think webrtc-pc should be updated to follow what
> JSEP says, and think we should merge the PR [b].
>
> The reason why is that the current webrtc-pc spec (in my opinion) is
> vague and that it assumes knowledge the sender does not have.
>
> Webrtc-pc [c] talks about a 'desired' video size, but what is desired is
> not defined. If the video track at the receiving end was displayed in a
> single video element, the dimensions of that element would probably be
> the 'desired' size, but first of all such dimensions are not signaled to
> the sender, and secondly it is easy to imagine situations where the
> video at the receiving end is displayed on several video elements of
> different dimensions.
>
> What _is_ signaled from receiver to sender (using the 'imageattr' SDP
> attribute) is video dimensions that the receiver supports [d], but that
> is not the same as the size of a video element but rather the
> capabilities of the receiver.
>
> The current text in webrtc-pc [c] is said to be made to "minimize
> occurrence of images with with letter box or or pillow boxing.", but as
> explained above that can't be made without knowledge of the dimensions
> of the rendering video element.
>
> Therefore I propose we remove the current text on 'centering, scaling,
> cropping', and instead reference JSEP section 3.6.2.
>
> Thoughts?
>
> //Stefan
>
> [a] https://github.com/w3c/webrtc-pc/issues/1283
> [b] https://github.com/w3c/webrtc-pc/pull/1570
> [c] https://w3c.github.io/webrtc-pc/#rtp-media-api
> [d] http://rtcweb-wg.github.io/jsep/#rfc.section.3.6.2
>
>