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Re: Proposal: align video scaling with JSEP

From: Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com>
Date: Mon, 2 Oct 2017 16:41:23 +0000
To: "Cullen Jennings (fluffy)" <fluffy@cisco.com>
CC: WebRTC WG <public-webrtc@w3.org>
Message-ID: <HE1PR07MB09700435F3363F914A5292C7C97D0@HE1PR07MB0970.eurprd07.prod.outlook.com>
On 02/10/17 18:30, Cullen Jennings (fluffy) wrote:
> 
>> On Sep 26, 2017, at 5:56 AM, Stefan Håkansson LK 
>> <stefan.lk.hakansson@ericsson.com <mailto:stefan.lk.hakansson@ericsson.com>> 
>> wrote:
>>
>> Therefore I propose we remove the current text on 'centering, scaling,
>> cropping', and instead reference JSEP section 3.6.2.
> 
> That is what we originally had and Martin and others complained that more advice
> was needed. I don't think we can change the current advice but it still seems we
> need to say something to have consistent behaviour between browsers. I do think
> consistent behaviour is important because removing this going to result in
> letter boxing and when one thing does it one way and something else does it
> another, you can end up with the situation with a black border all the way
> around the outside of image. Apps will need to know what the browser are going
> to do so that the application can compensate to achieve the desired outcome for
> the application.
> 
> I think EKR and Justin have argued for one of the principals being don't loose
> information by cropping as this is really bad in cases like screen share. They
> are also arguing for don't change aspect ration (other than minor bit caused by
> rounding error in scaling ).  So I think that means this needs to say something
> along the lines of black border is added to image to get to correct aspect
> ratio, then it is scaled to get to correct size.

Part of my reasoning is that the sender side does not (usually) know the 
rendering size on the remote end. All the sender knows is what the 
receiver is able to receive/decode, it does not know the rendering 
dimensions so it would be impossible to know if there would be a black 
border anywhere when this is eventually rendered. "Correct" size is 
unknown as I have understood it.
Received on Monday, 2 October 2017 16:41:50 UTC

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