NewPipe/app/src/main/java/org/schabi/newpipe/player/playback/PlaybackListener.java

package org.schabi.newpipe.player.playback;

import android.support.annotation.NonNull;
import android.support.annotation.Nullable;

import com.google.android.exoplayer2.source.MediaSource;

import org.schabi.newpipe.extractor.stream.StreamInfo;
import org.schabi.newpipe.playlist.PlayQueueItem;

import java.util.List;

public interface PlaybackListener {
    /**
     * Called when the stream at the current queue index is not ready yet.
     * Signals to the listener to block the player from playing anything and notify the source
     * is now invalid.
     *
     * May be called at any time.
     * */
    void block();

    /**
     * Called when the stream at the current queue index is ready.
     * Signals to the listener to resume the player by preparing a new source.
     *
     * May be called only when the player is blocked.
     * */
    void unblock(final MediaSource mediaSource);

    /**
     * Called when the queue index is refreshed.
     * Signals to the listener to synchronize the player's window to the manager's
     * window.
     *
     * May be called only after unblock is called.
     * */
    void sync(@NonNull final PlayQueueItem item, @Nullable final StreamInfo info);

    /**
     * Requests the listener to resolve a stream info into a media source
     * according to the listener's implementation (background, popup or main video player).
     *
     * May be called at any time.
     * */
    MediaSource sourceOf(final PlayQueueItem item, final StreamInfo info);

    /**
     * Called when the play queue can no longer to played or used.
     * Currently, this means the play queue is empty and complete.
     * Signals to the listener that it should shutdown.
     *
     * May be called at any time.
     * */
    void shutdown();
}