CanvasCaptureMediaStreamTrack.requestFrame() - Web APIs 编辑

The CanvasCaptureMediaStreamTrack method requestFrame() requests that a frame be captured from the canvas and sent to the stream. Applications that need to carefully control the timing of rendering and frame capture can use requestFrame() to directly specify when it's time to capture a frame.

To prevent automatic capture of frames, so that frames are only captured when requestFrame() is called, specify a value of 0 for the captureStream() method when creating the stream.

Syntax

stream.requestFrame();

Return value

undefined

Usage notes

There is currently an issue flagged in the specification pointing out that at this time, no exceptions are being thrown if the canvas isn't origin-clean. This may change in the future, so it would be wise to plan ahead and watch for exceptions such as SecurityError (although the specific error that might be thrown is not mentioned in the spec, this is a likely candidate).

Example

// Find the canvas element to capture
var canvasElt = document.getElementsByTagName("canvas")[0];

// Get the stream
var stream = canvasElt.captureStream(25); // 25 FPS

// Send the current state of the canvas as a frame to the stream
stream.getVideoTracks()[0].requestFrame();

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• CanvasCaptureMediaStream, the interface it belongs to.
• <canvas>