- From: Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com>
- Date: Tue, 26 Sep 2017 11:56:31 +0000
- To: WebRTC WG <public-webrtc@w3.org>
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
Received on Tuesday, 26 September 2017 11:57:07 UTC