android13/external/exoplayer/tree_15dc86382f17a24a3e881e52e31a810c1ea44b49/docs/playlists.md

title
Playlists

The playlist API is defined by the Player interface, which is implemented by all ExoPlayer implementations. It enables sequential playback of multiple media items. The following example shows how to start playback of a playlist containing two videos:

// Build the media items.
MediaItem firstItem = MediaItem.fromUri(firstVideoUri);
MediaItem secondItem = MediaItem.fromUri(secondVideoUri);
// Add the media items to be played.
player.addMediaItem(firstItem);
player.addMediaItem(secondItem);
// Prepare the player.
player.prepare();
// Start the playback.
player.play();

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Transitions between items in a playlist are seamless. There's no requirement that they're of the same format (e.g., it’s fine for a playlist to contain both H264 and VP9 videos). They may even be of different types (e.g., it’s fine for a playlist to contain both videos and audio only streams). It's allowed to use the same MediaItem multiple times within a playlist.

Modifying the playlist

It's possible to dynamically modify a playlist by adding, moving and removing media items. This can be done both before and during playback by calling the corresponding playlist API methods:

// Adds a media item at position 1 in the playlist.
player.addMediaItem(/* index= */ 1, MediaItem.fromUri(thirdUri));
// Moves the third media item from position 2 to the start of the playlist.
player.moveMediaItem(/* currentIndex= */ 2, /* newIndex= */ 0);
// Removes the first item from the playlist.
player.removeMediaItem(/* index= */ 0);

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Replacing and clearing the entire playlist are also supported:

// Replaces the playlist with a new one.
List<MediaItem> newItems = ImmutableList.of(
    MediaItem.fromUri(fourthUri),
    MediaItem.fromUri(fifthUri));
player.setMediaItems(newItems, /* resetPosition= */ true);
// Clears the playlist. If prepared, the player transitions to the ended state.
player.clearMediaItems();

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The player automatically handles modifications during playback in the correct way. For example if the currently playing media item is moved, playback is not interrupted and its new successor will be played upon completion. If the currently playing MediaItem is removed, the player will automatically move to playing the first remaining successor, or transition to the ended state if no such successor exists.

Querying the playlist

The playlist can be queried using Player.getMediaItemCount and Player.getMediaItemAt. The currently playing media item can be queried by calling Player.getCurrentMediaItem. There are also other convenience methods like Player.hasNextMediaItem or Player.getNextMediaItemIndex to simplify navigation in the playlist.

Repeat modes

The player supports 3 repeat modes that can be set at any time with Player.setRepeatMode:

• Player.REPEAT_MODE_OFF: The playlist isn't repeated and the player will transition to Player.STATE_ENDED once the last item in the playlist has been played.
• Player.REPEAT_MODE_ONE: The current item is repeated in an endless loop. Methods like Player.seekToNextMediaItem will ignore this and seek to the next item in the list, which will then be repeated in an endless loop.
• Player.REPEAT_MODE_ALL: The entire playlist is repeated in an endless loop.

Shuffle mode

Shuffle mode can be enabled or disabled at any time with Player.setShuffleModeEnabled. When in shuffle mode, the player will play the playlist in a precomputed, randomized order. All items will be played once and the shuffle mode can also be combined with Player.REPEAT_MODE_ALL to repeat the same randomized order in an endless loop. When shuffle mode is turned off, playback continues from the current item at its original position in the playlist.

Note that the indices as returned by methods like Player.getCurrentMediaItemIndex always refer to the original, unshuffled order. Similarly, Player.seekToNextMediaItem will not play the item at player.getCurrentMediaItemIndex() + 1, but the next item according to the shuffle order. Inserting new items in the playlist or removing items will keep the existing shuffled order unchanged as far as possible.

Setting a custom shuffle order

By default the player supports shuffling by using the DefaultShuffleOrder. This can be customized by providing a custom shuffle order implementation, or by setting a custom order in the DefaultShuffleOrder constructor:

// Set a custom shuffle order for the 5 items currently in the playlist:
exoPlayer.setShuffleOrder(
    new DefaultShuffleOrder(new int[] {3, 1, 0, 4, 2}, randomSeed));
// Enable shuffle mode.
exoPlayer.setShuffleModeEnabled(/* shuffleModeEnabled= */ true);

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Identifying playlist items

To identify playlist items, MediaItem.mediaId can be set when building the item:

// Build a media item with a media ID.
MediaItem mediaItem =
    new MediaItem.Builder().setUri(uri).setMediaId(mediaId).build();

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If an app does not explicitly define a media ID for a media item, the string representation of the URI is used.

Associating app data with playlist items

In addition to an ID, each media item can also be configured with a custom tag, which can be any app provided object. One use of custom tags is to attach metadata to each media item:

// Build a media item with a custom tag.
MediaItem mediaItem =
    new MediaItem.Builder().setUri(uri).setTag(metadata).build();

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Detecting when playback transitions to another media item

When playback transitions to another media item, or starts repeating the same media item, Listener.onMediaItemTransition(MediaItem, @MediaItemTransitionReason) is called. This callback receives the new media item, along with a @MediaItemTransitionReason indicating why the transition occurred. A common use case for onMediaItemTransition is to update the application's UI for the new media item:

@Override
public void onMediaItemTransition(
    @Nullable MediaItem mediaItem, @MediaItemTransitionReason int reason) {
  updateUiForPlayingMediaItem(mediaItem);
}

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If the metadata required to update the UI is attached to each media item using custom tags, then an implementation might look like:

@Override
public void onMediaItemTransition(
    @Nullable MediaItem mediaItem, @MediaItemTransitionReason int reason) {
  @Nullable CustomMetadata metadata = null;
  if (mediaItem != null && mediaItem.localConfiguration != null) {
    metadata = (CustomMetadata) mediaItem.localConfiguration.tag;
  }
  updateUiForPlayingMediaItem(metadata);
}

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Detecting when the playlist changes

When a media item is added, removed or moved, Listener.onTimelineChanged(Timeline, @TimelineChangeReason) is called immediately with TIMELINE_CHANGE_REASON_PLAYLIST_CHANGED. This callback is called even when the player has not yet been prepared.

@Override
public void onTimelineChanged(
    Timeline timeline, @TimelineChangeReason int reason) {
  if (reason == TIMELINE_CHANGE_REASON_PLAYLIST_CHANGED) {
    // Update the UI according to the modified playlist (add, move or remove).
    updateUiForPlaylist(timeline);
  }
}

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When information such as the duration of a media item in the playlist becomes available, the Timeline will be updated and onTimelineChanged will be called with TIMELINE_CHANGE_REASON_SOURCE_UPDATE. Other reasons that can cause a timeline update include:

• A manifest becoming available after preparing an adaptive media item.
• A manifest being updated periodically during playback of a live stream.