Media Session action types - Web APIs 编辑

To support an action on a media session, such as seeking, pausing, or changing tracks, you need to call the MediaSession interface's setActionHandler() method to establish a handler for that action. The specific type of media session action to be handled on a MediaSession is identified using a string from the MediaSessionAction enumerated type.

Syntax

A media session action's type is specified using a string from the MediaSessionAction enumerated type.

BCD tables only load in the browser

Each of the actions is a common media session control request. Implement support for each of these in order to allow that type of action to be performed. The following strings identify the currently available types of media session action:

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 MediaSessionActionDetails property seekOffset specifies the amount of time to seek backward.

seekforward

Seeks forward from the current position through the media. The MediaSessionActionDetails property seekOffset 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 MediaSessionActionDetails property seekTime. If you intend to perform multiple seekto operations in rapid succession, you can also specify the MediaSessionActionDetails property fastSeek property 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.

A media session action may be generated by any media session action source; these sources include anything from UI widgets within the browser itself to media control keys on the user's keyboard to buttons on the user's headset or earbuds.

This example implements seek forward and backward actions for an audio player by setting up the seekforward and seekbackward action handlers.

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

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

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

In this case, both the seekforward and seekbackward handlers are using a fixed distance, ignoring the time specified by the MediaSessionActionDetails passed into the handler.

You can also, if you prefer, use a single function to handle multiple action types, by checking the value of the MediaSessionActionDetails object's 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.

In this example, instead of seeking a specified distance, the seekforward and seekbackward handlers use the time specified in the MediaSessionActionDetails object's seekOffset property.

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

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