W3C home > Mailing lists > Public > public-webrtc@w3.org > February 2016

Re: maxHeight and maxWidth

From: Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com>
Date: Wed, 17 Feb 2016 07:13:21 +0000
To: Peter Thatcher <pthatcher@google.com>, Adam Roach <adam@nostrum.com>
CC: Randell Jesup <randell-ietf@jesup.org>, "public-webrtc@w3.org" <public-webrtc@w3.org>
Message-ID: <1447FA0C20ED5147A1AA0EF02890A64B37497DE3@ESESSMB209.ericsson.se>
On 17/02/16 03:38, Peter Thatcher wrote:
> While thinking about this so more, I thought of another difficulty: if
> resolution is degraded, should that degradation happen before or after
> the max?
>
> In your use case with two layers (1 full, 1 max of 90 pixels tall), what
> happens when the RtpSender degrades the resolution?   Let's say it
> degrades a video frame an original height of 360 pixels down to a height
> of 180 pixels.

Even when disregarding maxWidth/Height, I have the feeling this is an 
area that is underspecified today.

Assume the feed here is a video track constrained (mandatory) to be 360 
in height - no more no less. Is the rtpSender (assuming: no 
scaleResolutionDownBy applied) allowed to scale it down to 180? 
Presumably yes (for example if there is congestion), but there is no 
text saying it is allowed (OTOH there is no text saying it should strive 
for 360 either).

Now, add a simulcast stream with scaleResolutionDownBy = 4 meaning 90 
going out on the wire. Now if the rtpSender scales the base to 180, what 
does that mean for the simulcast stream? Is it scaled from 360 (the 
feeding MediaStreamTrack) or 180? It is not clear to me when reading the 
spec.
Received on Wednesday, 17 February 2016 07:14:02 UTC

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