Bug 299955 – [macOS Safari] Local and outgoing shared screen is not adjusted to the full screen when User resizes the shared window

• Component: WebRTC
• Status: RESOLVED FIXED

Created attachment 476921 [details]
Sysdiagnose file collected at 17:42:04, 2025.10.01, UTC+3 time zone

Summary:
[macOS Safari] Local and outgoing shared screen is not adjusted to the full screen when user resizes the shared window

Tested devices and browsers:
Bug is reproducible on:
- MacBook Pro (M1, 2020, macOS 26.0) and Safari 26.0 (21622.1.22.11.14)
- MacBook Pro (M1, 2020, macOS 15.6.1) and Safari 18.6 (20621.3.11.11.3)
- MacBook Pro (M1, 2020, macOS 14.6.1) and Safari 17.6 (19618.3.11.11.5)

Bug is NOT reproducible on:
- MacBook Pro (M1, 2020, macOS 26.0) and Google Chrome (141.0.7390.55)
- MacBook Pro (M1, 2020, macOS 15.6.1) and Google Chrome (139.0.7258.155)
- Lenovo ThinkPad E495 (Windows 11 Enterprise) and MS Edge (139.0.3405.125)

Use case:
Precondition:
Remote User is in an active WebRTC call

Steps:
1. User joins a call
2. User clicks "Start screen sharing" and chooses the "Share Window" option
3. User resizes the shared window
4. User observes the local screen sharing preview and Remote User observes incoming screen share

Actual result:
Local and outgoing shared screen video streams do NOT automatically resize to fill the entire video container when User resizes the shared window

Expected result:
Local and outgoing shared screen video streams automatically resize to fill the entire video container when User resizes the shared window

Reproducibility:
100%

Reproducibility with other services:
Bug is reproducible with WebRTC sample (https://webrtc.github.io/samples/src/content/getusermedia/getdisplaymedia/)
Bug is reproducible with teams.microsoft.com - only on Safari
Bug is NOT reproducible with Teams Desktop app
Bug is NOT reproducible with Google Meets

Additional information:
Sysdiagnostics file added (reproduced at 17:42:04, 2025.10.01, UTC+3 time zone):
sysdiagnose_2025.10.01_17-42-04+0300_macOS_Mac_25A362.tar.gz

Created attachment 476922 [details]
Screen recording of the issue

[Radar WebKit Bug Importer]

<rdar://problem/161736839>

[youenn fablet]

Pull request: https://github.com/WebKit/WebKit/pull/52112

[EWS]

Committed 301477@main (f2be77ec4f12): <https://commits.webkit.org/301477@main>

Reviewed commits have been landed. Closing PR #52112 and removing active labels.