The MediaRecorder() constructor creates a new MediaRecorder object that will record a specified MediaStream.
The MediaStream that will be recorded. This source media can come from a stream created using navigator.mediaDevices.getUserMedia() or from an <audio>, <video> or <canvas> element.
mimeType: The mime type you want to use as the recording container for the new MediaRecorder. Applications can check in advance if this mimeType is supported by the user agent by calling MediaRecorder.isTypeSupported().
audioBitsPerSecond: The chosen bitrate for the audio component of the media.
videoBitsPerSecond: The chosen bitrate for the video component of the media.
bitsPerSecond: The chosen bitrate for the audio and video components of the media. This can be specified instead of the above two properties. If this is specified along with one or the other of the above properties, this will be used for the one that isn't specified.
If bits per second values are not specified for video and/or audio, the default adopted for video is 2.5Mbps, while the audio default is adaptive, depending upon the sample rate and the number of channels.
This example shows how to create a media recorder for a specified stream, whose audio bit rate is set to 128Kbit/sec and whose video bit rate is set to 2.5 Mbit/sec. The recorded media data will be stored in an MP4 wrapper (so if you gather the chunks of media data and save them to disk, they will be in an MP4 file).
simpl.info MediaStream Recording demo, by Sam Dutton.