MediaSourceHandle

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

Note: This feature is available in Dedicated Web Workers.

The MediaSourceHandle interface of the Media Source Extensions API is a proxy for a MediaSource that can be transferred from a dedicated worker back to the main thread and attached to a media element via its HTMLMediaElement.srcObject property. MediaSource objects are not transferable because they are event targets, hence the need for MediaSourceHandles.

It can be accessed via the MediaSource.handle property.

Each MediaSource object created inside a dedicated worker has its own distinct MediaSourceHandle. The MediaSource.handle getter will always return the MediaSourceHandle instance specific to the associated dedicated worker MediaSource instance. If the handle has already been transferred to the main thread using postMessage(), the handle instance in the worker is technically detached and can't be transferred again.

MediaSourceHandle is a transferable object.

js
// Inside dedicated worker
let mediaSource = new MediaSource();
let handle = mediaSource.handle;
// Transfer the handle to the context that created the worker
postMessage({ arg: handle }, [handle]);

mediaSource.addEventListener("sourceopen", () => {
  // Await sourceopen on MediaSource before creating SourceBuffers
  // and populating them with fetched media — MediaSource won't
  // accept creation of SourceBuffers until it is attached to the
  // HTMLMediaElement and its readyState is "open"
});

Over in the main thread, we receive the handle via a message event handler, attach it to a <video> via its HTMLMediaElement.srcObject property, and play the video:

js
worker.addEventListener("message", (msg) => {
  let mediaSourceHandle = msg.data.arg;
  video.srcObject = mediaSourceHandle;
  video.play();
});

Note: MediaSourceHandles cannot be successfully transferred into or via a shared worker or service worker.

Specifications

Specification

Media Source Extensions™
# mediasourcehandle

Browser compatibility

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This page was last modified on Jun 24, 2025 by MDN contributors.

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Media Source API
MediaSourceHandle
Related pages for Media Source Extensions
Guides
1. Transcoding assets for Media Source Extensions
2. DASH Adaptive Streaming for HTML video

MediaSourceHandle

In this article

Instance properties

Instance methods

Examples

Specifications

Browser compatibility

See also

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