1703991 - getDisplayMedia() doesn't downscale by source pixel ratio by default

Status: NEW

(Core :: WebRTC: Audio/Video, defect, P3)

Description

[Jan-Ivar Bruaroey [:jib] (needinfo? me)]

The spec says: "The user agent SHOULD downscale by the source pixel ratio by default, unless otherwise directed by applied constraints."

I.e. on Retina macs where window.devicePixelRatio is 2, we should halve the width and height of unconstrained capture.

STRs:

1. https://jsfiddle.net/jib1/5e1cbpyt/show

Expected result (Chrome):

• 1536 x 960

Actual result (Firefox):

• 3072 x 1920

Comment 1

[Jan-Ivar Bruaroey [:jib] (needinfo? me)]

We're seeing performance issues with 4K, so we should up-prioritize this.

Comment 2

[Jan-Ivar Bruaroey [:jib] (needinfo? me)]

With https://jsfiddle.net/jib1/pc8yedw6/ (Click Go & share Entire Screen) I see this difference on my 2019 MBP with macOS 10.15.7 (19H1030):

• Firefox (1536 x 960): Framerate: ~8
• Chrome (1536 x 960): Framerate: ~29

That fiddle already downscales to 1536 x 960 using constraints, which suggests that fixing this bug likely won't help, and that the underlying problem is likely deeper, as suggested in bug 1703522 comment 4.

Comment 3

[Andreas Pehrson [:pehrsons]]

This shouldn't be too hard to fix, and makes the resizeMode handling complete in bug 1286945.

Comment 4

[Andreas Pehrson [:pehrsons]]

A tad bit more complicated than I thought, because the libwebrtc capturers only tag frames with the appropriate scaling number on Windows.