MediaRecorder: mimeType property

The mimeType read-only property of the MediaRecorder interface returns the MIME media type that was specified when creating the MediaRecorder object, or, if none was specified, which was chosen by the browser. This is the file format of the file that would result from writing all of the recorded data to disk.

Keep in mind that not all codecs are supported by a given container; if you write media using a codec that is not supported by a given media container, the resulting file may not work reliably if at all when you try to play it back. See our media type and format guide for information about container and codec support across browsers.

Note: The term "MIME type" is officially considered to be historical; these strings are now officially known as media types. MDN Web Docs content uses the terms interchangeably.

Value

The MIME media type which describes the format of the recorded media, as a string. This string may include the codecs parameter, giving details about the codecs and the codec configurations used by the media recorder.

The media type strings are standardized by the Internet Assigned Numbers Authority (IANA). For their official list of defined media type strings, see the article Media Types on the IANA site. See also media types to learn more about media types and how they're used in web content and by web browsers.

Examples

if (navigator.mediaDevices) {
  console.log("getUserMedia supported.");

  const constraints = { audio: true, video: true };
  const chunks = [];

  navigator.mediaDevices
    .getUserMedia(constraints)
    .then((stream) => {
      const options = {
        audioBitsPerSecond: 128000,
        videoBitsPerSecond: 2500000,
        mimeType: "video/mp4",
      };
      const mediaRecorder = new MediaRecorder(stream, options);
      m = mediaRecorder;

      m.mimeType; // would return 'video/mp4'
      // …
    })
    .catch((error) => {
      console.error(error.message);
    });
}

Changing the mimeType in options to 'video/mp4; codecs="avc1.424028, mp4a.40.2"' causes MediaRecorder to try to use AVC Constrained Baseline Profile Level 4 for video and AAC-LC (Low Complexity) for audio, which is good for mobile and other possible resource-constrained situations.

Assuming this configuration is acceptable to the user agent, the value returned later by m.mimeType would then be video/mp4; codecs="avc1.424028, mp4a.40.2".

Specifications

Specification
MediaStream Recording # dom-mediarecorder-mimetype

Browser compatibility

BCD tables only load in the browser