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Re: maxHeight and maxWidth

From: Jan-Ivar Bruaroey <jib@mozilla.com>
Date: Wed, 17 Feb 2016 13:15:16 -0500
To: Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com>, 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: <56C4B8B4.2070809@mozilla.com>
On 2/17/16 2:13 AM, Stefan Håkansson LK wrote:
> 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).

FWIW there's a picture in the Media Capture and Stream spec [1] that 
suggests a peer connection can do whatever it wants with the resolution.

Underspecified, I would agree (unless I missed some recent developments, 
which is possible).

> 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.

When doing simulcast I believe what you call the "base" and the highest 
fidelity simulcast stream are the same thing, so there's no double scaling.

[1] 
http://w3c.github.io/mediacapture-main/getusermedia.html#the-model-sources-sinks-constraints-and-settings

.: Jan-Ivar :.
Received on Wednesday, 17 February 2016 18:15:47 UTC

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