HTMLCanvasElement: captureStream() method

The captureStream() method of the HTMLCanvasElement interface returns a MediaStream which includes a CanvasCaptureMediaStreamTrack containing a real-time video capture of the canvas's contents.

Syntax

captureStream()
captureStream(frameRate)

Parameters

frameRate Optional

A double-precision floating-point value that indicates the rate of capture of each frame. If not set, a new frame will be captured each time the canvas changes; if set to 0, frames will not be captured automatically; instead, they will only be captured when the returned track's requestFrame() method is called.

Return value

A reference to a MediaStream object, which has a single CanvasCaptureMediaStreamTrack in it.

Exceptions

NotSupportedError DOMException

Thrown if the value of frameRate is negative.

SecurityError DOMException

The canvas's bitmap is not origin clean; at least some of its contents have or may have been loaded from a site other than the one from which the document itself was loaded.

Example

// Find the canvas element to capture
const canvasElt = document.querySelector("canvas");
// Get the stream
const stream = canvasElt.captureStream(25); // 25 FPS
// Do things to the stream
// E.g. Send it to another computer using an RTCPeerConnection
// pc is an RTCPeerConnection created elsewhere
stream.getTracks().forEach((track) => pc.addTrack(track, stream));

Specifications

Browser compatibility

See also

• HTMLMediaElement.captureStream(), which allows capturing a stream from a media element.
• MediaStream
• Media Capture and Streams API