mimeType property

The mimeType read-only property of the MediaRecorder interface returns the 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.