HTMLMediaElement.captureStream()

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The captureStream() property of the HTMLMediaElement interface returns a MediaStream object which is streaming a real-time capture of the content being rendered in the media element.

This can be used, for example, as a source for a WebRTC RTCPeerConnection.

Syntax

var mediaStream = mediaElement.captureStream()

Parameters

None.

Return value

MediaStream object which can be used as a source for audio and/or video data by other media processing code, or as a source for WebRTC.

Example

In this example, an event handler is established so that clicking a button starts capturing the contents of a media element with the ID "playback" into a MediaStream. The stream can then be used for other purposes—like a source for streaming over WebRTC, to allow sharing prerecorded videos with another person during a video call.

document.querySelector('.playAndRecord').addEventListener('click', function() {
  var playbackElement = document.getElementById("playback");
  var captureStream = playbackElement.captureStream();
  playbackElement.play();
});

See Recording a media element for a longer and more intricate example and explanation.

Specifications

Specification Status Comment
Media Capture from DOM Elements
The definition of 'captureStream()' in that specification.
Working Draft Initial definition.

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
Basic supportChrome Full support 53Edge No support NoFirefox Full support 15
Prefixed
Full support 15
Prefixed
Prefixed Implemented with the vendor prefix: moz
IE No support NoOpera ? Safari No support NoWebView Android Full support 53Chrome Android Full support 53Edge Mobile No support NoFirefox Android Full support 15
Prefixed
Full support 15
Prefixed
Prefixed Implemented with the vendor prefix: moz
Opera Android ? Safari iOS No support NoSamsung Internet Android ?

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
Requires a vendor prefix or different name for use.
Requires a vendor prefix or different name for use.

Firefox-specific notes

Prior to Firefox 51, you couldn't use captureStream() on a media element whose source is, itself, a MediaStream (like a <video> element which is presenting a stream being received over a RTCPeerConnection). Beginning in Firefox 51, this works. This means you can capture a stream from the video element and use MediaRecorder to record it. See bug 1259788 for details.

However, captureStream() is still prefixed as mozCaptureStream() on Firefox for good reason: there are some quirks in the present implementation which are worth noting:

  • The Firefox implementation currently only works as described in the specification when the media element's source is, itself, a MediaStream.
  • If the media element's source isn't a MediaStream, the output from this method isn't compatible with the spec, and if you change the source after starting capture, the output capture stream can't accept the new source data due to that incompatibility, so no MediaStreamTracks from the new source MediaStream are added to the captured stream, resulting in output that doesn't capture the updated source.
  • Switching the source back to a MediaStream adds tracks back to the stream and it works again as expected.
  • Calling mozCaptureMediaStream() on an element with a MediaStream source returns a stream that only contains tracks while the element is playing a MediaStream.
  • If you call mozCaptureMediaStream() on a media element with no source media, its compatibility mode will be based on the first source that's added; for example, if it's a MediaStream, then the capture stream will only work with MediaStream sources from then on.
  • This special behavior will be removed once the non-MediaStream source support is brought up to specification and the method is unprefixed. See bug 1259788, comment 160 for details.

See also

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