The HTMLMediaElement.playbackRate property sets the rate at which the media is being played back. This is used to implement user controls for fast forward, slow motion, and so forth. The normal playback rate is multiplied by this value to obtain the current rate, so a value of 1.0 indicates normal speed.
The HTMLMediaElement.defaultMuted property reflects the muted HTML attribute, which indicates whether the media element's audio output should be muted by default. This property has no dynamic effect. To mute and unmute the audio output, use the muted property.
The HTMLMediaElement interface adds to HTMLElement the properties and methods needed to support basic media-related capabilities that are common to audio and video. The HTMLVideoElement and HTMLAudioElement elements both inherit this interface.