Intent to Ship: [WebRTC] RTCRtpEncodingParameters.scaleResolutionDownTo

[Henrik Boström]

Contact emails

hb...@chromium.org

Specification

https://w3c.github.io/webrtc-extensions/#dom-rtcrtpencodingparameters-scaleresolutiondownto

Summary

An API that configures WebRTC encoders to scale input frames if they are greater than the specified maxWidth and maxHeight. This API is similar to scaleResolutionDownBy except that resolution constraints are expressed in absolute terms (e.g. 640x360) as opposed to relative terms (e.g. scale down by 2), avoiding race conditions related to changing input frame size on the fly.

In particular, when simulcast is used to send multiple resolutions (e.g. 720p + 360p), the app may dynamically turn the top layer(s) on and off. Having an API that gives the app a race-free way to adjust the track resolution accordingly can have big performance wins, e.g. video effects processing on a 360p track instead of a 720p track when all we're sending is 360p. The old way to do this "scale down by factor X" is racy when track resolution changes dynamically (e.g. momentarily doing 360p + 180p or temporarily disabling encoding), which is not ideal for receive side quality. Not nice API ergonomics either.

Blink component

Blink>WebRTC>PeerConnection

TAG review status

Not applicable - small addition to existing API

Risks

Interoperability and Compatibility

None assuming all browsers implement this, otherwise the app can always fall back to the old way of configuring scaling factors (the scaleResolutionDownBy API)

Gecko: https://github.com/mozilla/standards-positions/issues/1071

WebKit: https://github.com/WebKit/standards-positions/issues/396

Web developers:

Positive (hearts and positive feedback on issue and positively received in Virtual Interim)

WebView application risks

None

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?

Yes

Is this feature fully tested by web-platform-tests?

Yes

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5206373705711616?gate=5103417056559104

[Henrik Boström]

Forgot to link but here are the notes + recordings from the virtual interim: https://www.w3.org/2024/08/27-webrtc-minutes.html#t06

[Alex Russell]

LGTM1

[Mike Taylor]

LGTM2

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[Daniel Bratell]

LGTM3

/Daniel

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