MediaSource in Worker

The Videos team at Facebook has a growing need to move calls to Media Source Extensions off of the main thread and into a Worker. While most parts of your off-the-shelve streaming video player can be implemented in a Worker (fetching and parsing of the manifest as well as selecting and fetching of segments) the calls to and interactions with the Media Source Extensions API (e.g. SourceBuffer.prototype.appendBuffer, SourceBuffer.prototype.remove, etc) remain a bottleneck and have to happen on the main browser rendering thread.

On a sizable and complex web site large blocks of JS execution can regularly block the main thread making videos slow to start playing and causing lots of rebuffering, especially in live videos where you can only buffer ahead very little data. To ensure great web video performance in the long run, even as web apps continue to grow in size and complexity, we believe we need to allow video players to move into Workers and off of the main thread.

We would like to propose this change to the working group and involve other API users as well as implementors in the discussion.