The MediaRecorder.requestData() method (part of the MediaStream Recording API) is used to raise a dataavailable event containing a Blob object of the captured media as it was when the method was called. This can then be grabbed and manipulated as you wish.

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

1. If MediaRecorder.state is "inactive", raise a DOM InvalidState error and terminate these steps. If MediaRecorder.state is not "inactive", continue to the next step.
2. Raise a dataavailable event containing a Blob of the currently captured data (the Blob is available under the event's data attribute.)
3. Create a new Blob and place subsequently captured data into it.

None.

None (undefined).

An InvalidState error is raised if the requestData() method is called while the MediaRecorder object's MediaRecorder.state is not "recording" — the media cannot be captured if recording is not occurring.

• Using the MediaStream Recording 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