MediaRecorder: MediaRecorder() constructor

Syntax

new MediaRecorder(stream)
new MediaRecorder(stream, options)

Parameters

stream

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.

options Optional

A dictionary object that can contain the following properties:

mimeType Optional

A MIME type specifying the format for the resulting media; you may specify the container format (the browser will select its preferred codecs for audio and/or video), or you may use the codecs parameter and/or the profiles parameter to provide detailed information about which codecs to use and how to configure them. Applications can check in advance if a mimeType is supported by the user agent by calling MediaRecorder.isTypeSupported(). Defaults to an empty string.

audioBitsPerSecond Optional

The chosen bitrate for the audio component of the media.

videoBitsPerSecond Optional

The chosen bitrate for the video component of the media.

bitsPerSecond Optional

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.

audioBitrateMode Optional

The bitrate mode that should be used to encode the audio. Can be constant, which indicates that the recorder should encode at a constant bitrate, or variable, which indicates that the recorder should encode using a variable bitrate, thus allowing more space to be used for complex signals and less space for less-complex signals. Defaults to variable.

videoKeyFrameIntervalDuration Optional

The nominal interval in time between key frames in the encoded video stream. The user agent controls key-frame generation based on this option and the videoKeyFrameIntervalCount option.

videoKeyFrameIntervalCount Optional

The interval in number of frames between key frames in the encoded video stream. The user agent controls key-frame generation considering this option as well as videoKeyFrameIntervalDuration option.

Note: 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.

Note: Video resolution, frame rate and similar settings are specified as constraints when calling getUserMedia(), not here in the MediaStream Recording API.

Exceptions

NotSupportedError DOMException

Thrown if the specified MIME type is not supported by the user agent.

Examples

This example shows how to create a media recorder for a specified stream, whose audio bit rate is set to 128 Kbit/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).

if (navigator.mediaDevices.getUserMedia) {
  const constraints = { audio: true, video: true };
  const chunks = [];

  const onSuccess = (stream) => {
    const options = {
      audioBitsPerSecond: 128000,
      videoBitsPerSecond: 2500000,
      mimeType: "video/mp4",
    };
    const mediaRecorder = new MediaRecorder(stream, options);
    m = mediaRecorder;

    // …
  };
}

Specifications

Browser compatibility

See also

• 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.
• MediaDevices.getUserMedia