The MediaRecorder.start() method (part of the MediaRecorder API) is used to start capturing media into a Blob.

When the start() method is invoked, the UA queues a task that runs the following steps:

  1. If the MediaRecorder.state is not "inactive", raise a DOM InvalidState error and terminate these steps. if the MediaRecorder.state is "inactive", continue on to the next step.
  2. Set the MediaRecorder.state to "recording" and wait until media becomes available from the stream passed into Navigator.getUserMedia.
  3. Once data becomes available, raise a MediaRecorder.start event and start gathering the data into a Blob (see FILE-API).
  4. If the timeSlice argument has been provided, once that many milliseconds of data have been collected — or a minimum time slice imposed by the UA, whichever is greater — raise a MediaRecorder.dataavailable event containing the Blob of collected data, and start gathering a new Blob of data. If timeSlice has not been provided, continue gathering data into the original Blob.
  5. When the stream is ended, set MediaRecorder.state to "inactive" and stop gathering data.
  6. Raise a MediaRecorder.dataavailable event containing the Blob of data.
  7. Raise a MediaRecorder.stop event.

Note: If the browser is unable to start recording or continue recording, it will raise a DOMError event, followed by a MediaRecorder.dataavailable event containing the Blob it has gathered, followed by the MediaRecorder.stop event.




timeslice Optional
This parameter takes a value of milliseconds, and represents the length of media capture to return in each Blob. If it is not specified, all media captured will be returned in a single Blob, unless one or more calls are made to MediaRecorder.requestData.


An InvalidState error is raised if the start() method is called while the MediaRecorder object’s MediaRecorder.state is not "inactive" — it makes no sense to start media capture if it is already happening.



  record.onclick = function() {
    console.log("recorder started");



Specification Status Comment
MediaStream Recording
The definition of 'MediaRecorder.start()' in that specification.
Working Draft Initial definition

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 47 25.0 (25.0) No support No support No support
Feature Android Android Webview Firefox Mobile (Gecko) Firefox OS IE Phone Opera Mobile Safari Mobile Chrome for Android
Basic support No support 47 25.0 (25.0) 1.3[1] No support No support No support 47

[1] The intial Firefox OS implementation only supported audio recording.

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

API Media Capture Media Recorder API MediaRecorder Method Reference start