files/en-us/web/api/mediasource/handle/index.md
{{APIRef("Media Source Extensions")}}{{AvailableInWorkers("dedicated")}}
The handle read-only property of the {{domxref("MediaSource")}} interface returns a {{domxref("MediaSourceHandle")}} object, a proxy for the MediaSource that can be transferred from a dedicated worker back to the main thread and attached to a media element via its {{domxref("HTMLMediaElement.srcObject")}} property.
[!NOTE]
handleis only visible on {{domxref("MediaSource")}} instances inside dedicated workers.
Each MediaSource object created inside a dedicated worker has its own distinct MediaSourceHandle. The 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 {{domxref("DedicatedWorkerGlobalScope.postMessage()", "postMessage()")}}, the handle instance in the worker is technically detached and can't be transferred again.
A {{domxref("MediaSourceHandle")}} object instance.
The handle property can be accessed inside a dedicated worker and the resulting {{domxref("MediaSourceHandle")}} object is then transferred over to the thread that created the worker (in this case the main thread) via a {{domxref("DedicatedWorkerGlobalScope.postMessage()", "postMessage()")}} call:
// 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 {{domxref("Worker.message_event", "message")}} event handler, attach it to a {{htmlelement("video")}} via its {{domxref("HTMLMediaElement.srcObject")}} property, and {{domxref("HTMLMediaElement.play()", "play")}} the video:
worker.addEventListener("message", (msg) => {
let mediaSourceHandle = msg.data.arg;
video.srcObject = mediaSourceHandle;
video.play();
});
[!NOTE] {{domxref("MediaSourceHandle")}}s cannot be successfully transferred into or via a shared worker or service worker.
{{Specifications}}
{{Compat}}