The setActionHandler() method of the MediaSession interface sets a handler for a media session action. These actions let a web app receive notifications when the user engages a device's built-in physical or onscreen media controls, such as play, stop, or seek buttons.

type

A string representing an action type to listen for. It will be one of the following:

nexttrack

Advances playback to the next track.

pause

Pauses playback of the media.

play

Begins (or resumes) playback of the media.

previoustrack

Moves back to the previous track.

seekbackward

Seeks backward through the media from the current position. The seekOffset property passed to the callback specifies the amount of time to seek backward.

seekforward

Seeks forward from the current position through the media. The seekOffset property passed to the callback specifies the amount of time to seek forward.

seekto

Moves the playback position to the specified time within the media. The time to which to seek is specified in the seekTime property passed to the callback. If you intend to perform multiple seekto operations in rapid succession, you can also specify the fastSeek property passed to the callback with a value of true. This lets the browser know it can take steps to optimize repeated operations, and is likely to result in improved performance.

skipad

Skips past the currently playing advertisement or commercial. This action may or may not be available, depending on the platform and user agent, or may be disabled due to subscription level or other circumstances.

stop

Halts playback entirely.

callback

A function to call when the specified action type is invoked. The callback should not return a value. The callback receives a dictionary containing the following properties:

action

A string representing the action type. This property allows a single callback to handle multiple action types.

fastSeek Optional

A seekto action may optionally include this property, which is a Boolean value indicating whether or not to perform a "fast" seek. A "fast" seek is a seek being performed in a rapid sequence, such as when fast-forwarding or reversing through the media, rapidly skipping through it. This property can be used to indicate that you should use the shortest possible method to seek the media. fastSeek is not included on the final action in the seek sequence in this situation.

seekOffset Optional

If the action is either seekforward or seekbackward and this property is present, it is a floating point value which indicates the number of seconds to move the play position forward or backward. If this property isn't present, those actions should choose a reasonable default distance to skip forward or backward (such as 7 or 10 seconds).

seekTime Optional

If the action is seekto, this property must be present and must be a floating-point value indicating the absolute time within the media to move the playback position to, where 0 indicates the beginning of the media. This property is not present for other action types.

undefined.

To remove a previously-established action handler, call setActionHandler() again, specifying null as the callback.

The action handler receives as input a single parameter: an object which provides both the action type (so the same function can handle multiple action types), as well as data needed in order to perform the action.

This example creates a new media session and assigns action handlers (which don't do anything) to it.

if ('mediaSession' in navigator) {
  navigator.mediaSession.metadata = new MediaMetadata({
    title: 'Unforgettable',
    artist: 'Nat King Cole',
    album: 'The Ultimate Collection (Remastered)',
    artwork: [
      { src: 'https://dummyimage.com/96x96',   sizes: '96x96',   type: 'image/png' },
      { src: 'https://dummyimage.com/128x128', sizes: '128x128', type: 'image/png' },
      { src: 'https://dummyimage.com/192x192', sizes: '192x192', type: 'image/png' },
      { src: 'https://dummyimage.com/256x256', sizes: '256x256', type: 'image/png' },
      { src: 'https://dummyimage.com/384x384', sizes: '384x384', type: 'image/png' },
      { src: 'https://dummyimage.com/512x512', sizes: '512x512', type: 'image/png' },
    ]
  });

  navigator.mediaSession.setActionHandler('play', function() { /* Code excerpted. */ });
  navigator.mediaSession.setActionHandler('pause', function() { /* Code excerpted. */ });
  navigator.mediaSession.setActionHandler('stop', function() { /* Code excerpted. */ });
  navigator.mediaSession.setActionHandler('seekbackward', function() { /* Code excerpted. */ });
  navigator.mediaSession.setActionHandler('seekforward', function() { /* Code excerpted. */ });
  navigator.mediaSession.setActionHandler('seekto', function() { /* Code excerpted. */ });
  navigator.mediaSession.setActionHandler('previoustrack', function() { /* Code excerpted. */ });
  navigator.mediaSession.setActionHandler('nexttrack', function() { /* Code excerpted. */ });
  navigator.mediaSession.setActionHandler('skipad', function() { /* Code excerpted. */ });
}

The following example sets up two functions for playing and pausing, then uses them as callbacks with the relevant action handlers.

const actionHandlers = [
  // play
  [
    'play',
    async function() {
      // play our audio
      await audioEl.play();
      // set playback state
      navigator.mediaSession.playbackState = "playing";
      // update our status element
      updateStatus(allMeta[index], 'Action: play  |  Track is playing...')
    }
  ],
  [
    'pause',
    () => {
      // pause out audio
      audioEl.pause();
      // set playback state
      navigator.mediaSession.playbackState = "paused";
      // update our status element
      updateStatus(allMeta[index], 'Action: pause  |  Track has been paused...');
    }
  ],
]

for (const [action, handler] of actionHandlers) {
  try {
    navigator.mediaSession.setActionHandler(action, handler);
  } catch (error) {
    console.log(`The media session action "${action}" is not supported yet.`);
  }
}

This example uses appropriate action handlers to allow seeking in either direction through the playing media.

let skipTime = 10; // Time to skip in seconds

navigator.mediaSession.setActionHandler('seekbackward', evt => {
 // User clicked "Seek Backward" media notification icon.
 audio.currentTime = Math.max(audio.currentTime - skipTime, 0);
});

navigator.mediaSession.setActionHandler('seekforward', evt => {
 // User clicked "Seek Forward" media notification icon.
 audio.currentTime = Math.min(audio.currentTime + skipTime,
               audio.duration);
});

To remove a media action handler, assign it to null.

navigator.mediaSession.setActionHandler('nexttrack', null);

You can also, if you prefer, use a single function to handle multiple action types, by checking the value of the action property:

let skipTime = 7;

navigator.mediaSession.setActionHandler("seekforward", handleSeek);
navigator.mediaSession.setActionHandler("seekbackward", handleSeek);

function handleSeek(details) {
  switch(details.action) {
    case "seekforward":
      audio.currentTime = Math.min(audio.currentTime + skipTime,
              audio.duration);
      break;
    case "seekbackward":
      audio.currentTime = Math.max(audio.currentTime - skipTime, 0);
      break;
  }
}

Here, the handleSeek() function handles both seekbackward and seekforward actions.