MSE-in-Workers

[wolenetz]

Request for position on an emerging web specification

• WebKittens who can provide input: @jernoble @jyavenard

Information about the spec

• Spec Title: Media Source Extensions, specifically the sub-feature in MSEv2, "MSE-in-Workers"
• Spec URL: https://www.w3.org/TR/media-source-2/
• GitHub repository: https://github.com/w3c/media-source/
• Issue Tracker (if not the repository's issue tracker): MediaSource in Worker w3c/media-source#175
• Explainer: https://github.com/wicg/media-source/blob/mse-in-workers-using-handle/mse-in-workers-using-handle-explainer.md

Design reviews and vendor positions

• TAG Design Review: MSE-in-Workers w3ctag/design-reviews#656
• Mozilla standards-positions issue: MSE in Workers mozilla/standards-positions#547

Anything else we need to know

See also the previous request for position in 2021 on the webkit-dev list: https://lists.webkit.org/pipermail/webkit-dev/2021-June/031916.html

This feature addition to the Media Source Extensions specification enables web apps to use the MSE API in a DedicatedWorker. The app can attach a worker MediaSource object to a window/main context HTMLMediaElement by obtaining a MediaSourceHandle from the MediaSource object, transferring it to the window/main context, and setting that handle on the media element's srcObject attribute. This feature's specification has iterated in the W3C Media Workgroup, and has incorporated all feedback received to date. Experimental implementation in Chrome has already been reported to produce strongly positive metrics improvements by at least one origin trial site, due to the ability to perform media fetching and buffering in a worker context without blocking so much on a busy main/window context.