MediaRecorder.start

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.

Syntax

MediaRecorder.start(timeslice)

Parameters

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.

Errors

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.

Example

...

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

...

Specifications

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

Browser compatibility

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

See also

• Using the MediaRecorder API
• Web Dictaphone: MediaRecorder + getUserMedia + Web Audio API visualization demo, by Chris Mills (source on Github.)
• simpl.info MediaStream Recording demo, by Sam Dutton.
• Navigator.getUserMedia