Web-Facing Change PSA: Cross-Tab Region Capture
Elad Alon
Contact emails
Specification
https://w3c.github.io/mediacapture-region/
Summary
Using the (pre-existing) Screen Capture API, Web applications can prompt the user to screen-share a tab, a window or a screen, resulting in a MediaStream that contains a video MediaStreamTrack that can be consumed locally or transmitted remotely. Further, Web applications can use the (pre-existing) Region Capture API to crop this video track, removing all pixels that fall outside the bounding box of a target element; this is done using the MediaStreamTrack.cropTo() method, which accepts as input a CropTarget object that is associated with said “target element”.
Previously, successful calls to cropTo() would require:
The target element is within the captured tab.
The captured tab is the capturing tab. (That is, the app is capturing its own tab.)
Following a spec change made three years ago, and following a consultation with Chrome Security, the second of these two conditions is now being removed, starting m142. (There is, of course, no intention of ever removing the first.)
Risks
Interoperability and Compatibility
Gecko: No signal (Their representative Jan-Ivar Bruaroey approved merging the aforementioned PR into the spec back in 2022.)
WebKit: No signal (Their representative Youenn Fablet approved merging the aforementioned PR into the spec back in 2022.)
Flag name on about://flags
chrome://flags/#region-capture-cross-tab
Finch feature name
RegionCaptureOfOtherTabs
Sample links
https://eladalon1983.github.io/cross-tab-region-capture/