content: /*
   * Copyright (C) 2016 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package com.google.android.exoplayer2.trackselection;
  
  import static com.google.android.exoplayer2.util.Assertions.checkStateNotNull;
  
  import androidx.annotation.CallSuper;
  import androidx.annotation.Nullable;
  import com.google.android.exoplayer2.ExoPlaybackException;
  import com.google.android.exoplayer2.ExoPlayer;
  import com.google.android.exoplayer2.Player;
  import com.google.android.exoplayer2.Renderer;
  import com.google.android.exoplayer2.RendererCapabilities;
  import com.google.android.exoplayer2.RendererConfiguration;
  import com.google.android.exoplayer2.Timeline;
  import com.google.android.exoplayer2.audio.AudioAttributes;
  import com.google.android.exoplayer2.source.MediaSource.MediaPeriodId;
  import com.google.android.exoplayer2.source.TrackGroupArray;
  import com.google.android.exoplayer2.upstream.BandwidthMeter;
  
  /**
   * The component of an {@link ExoPlayer} responsible for selecting tracks to be consumed by each of
   * the player's {@link Renderer}s. The {@link DefaultTrackSelector} implementation should be
   * suitable for most use cases.
   *
   * <h2>Interactions with the player</h2>
   *
   * The following interactions occur between the player and its track selector during playback.
   *
   * <ul>
   *   <li>When the player is created it will initialize the track selector by calling {@link
   *       #init(InvalidationListener, BandwidthMeter)}.
   *   <li>When the player needs to make a track selection it will call {@link
   *       #selectTracks(RendererCapabilities[], TrackGroupArray, MediaPeriodId, Timeline)}. This
   *       typically occurs at the start of playback, when the player starts to buffer a new period of
   *       the media being played, and when the track selector invalidates its previous selections.
   *   <li>The player may perform a track selection well in advance of the selected tracks becoming
   *       active, where active is defined to mean that the renderers are actually consuming media
   *       corresponding to the selection that was made. For example when playing media containing
   *       multiple periods, the track selection for a period is made when the player starts to buffer
   *       that period. Hence if the player's buffering policy is to maintain a 30 second buffer, the
   *       selection will occur approximately 30 seconds in advance of it becoming active. In fact the
   *       selection may never become active, for example if the user seeks to some other period of
   *       the media during the 30 second gap. The player indicates to the track selector when a
   *       selection it has previously made becomes active by calling {@link
   *       #onSelectionActivated(Object)}.
   *   <li>If the track selector wishes to indicate to the player that selections it has previously
   *       made are invalid, it can do so by calling {@link
   *       InvalidationListener#onTrackSelectionsInvalidated()} on the {@link InvalidationListener}
   *       that was passed to {@link #init(InvalidationListener, BandwidthMeter)}. A track selector
   *       may wish to do this if its configuration has changed, for example if it now wishes to
   *       prefer audio tracks in a particular language. This will trigger the player to make new
   *       track selections. Note that the player will have to re-buffer in the case that the new
   *       track selection for the currently playing period differs from the one that was invalidated.
   *       Implementing subclasses can trigger invalidation by calling {@link #invalidate()}, which
   *       will call {@link InvalidationListener#onTrackSelectionsInvalidated()}.
   *   <li>When the player is {@linkplain Player#release() released}, it will release the track
   *       selector by calling {@link #release()}.
   * </ul>
   *
   * <h2>Renderer configuration</h2>
   *
   * The {@link TrackSelectorResult} returned by {@link #selectTracks(RendererCapabilities[],
   * TrackGroupArray, MediaPeriodId, Timeline)} contains not only {@link TrackSelection}s for each
   * renderer, but also {@link RendererConfiguration}s defining configuration parameters that the
   * renderers should apply when consuming the corresponding media. Whilst it may seem counter-
   * intuitive for a track selector to also specify renderer configuration information, in practice
   * the two are tightly bound together. It may only be possible to play a certain combination tracks
   * if the renderers are configured in a particular way. Equally, it may only be possible to
   * configure renderers in a particular way if certain tracks are selected. Hence it makes sense to
   * determine the track selection and corresponding renderer configurations in a single step.
   *
   * <h2>Threading model</h2>
   *
   * All calls made by the player into the track selector are on the player's internal playback
   * thread. The track selector may call {@link InvalidationListener#onTrackSelectionsInvalidated()}
   * from any thread.
   */
  public abstract class TrackSelector {
  
    /** Notified when selections previously made by a {@link TrackSelector} are no longer valid. */
    public interface InvalidationListener {
  
      /**
       * Called by a {@link TrackSelector} to indicate that selections it has previously made are no
       * longer valid. May be called from any thread.
       */
      void onTrackSelectionsInvalidated();
    }
  
    @Nullable private InvalidationListener listener;
    @Nullable private BandwidthMeter bandwidthMeter;
  
    /**
     * Called by the player to initialize the selector.
     *
     * @param listener An invalidation listener that the selector can call to indicate that selections
     *     it has previously made are no longer valid.
     * @param bandwidthMeter A bandwidth meter which can be used by track selections to select tracks.
     */
    @CallSuper
    public void init(InvalidationListener listener, BandwidthMeter bandwidthMeter) {
      this.listener = listener;
      this.bandwidthMeter = bandwidthMeter;
    }
  
    /**
     * Called by the player to release the selector. The selector cannot be used until {@link
     * #init(InvalidationListener, BandwidthMeter)} is called again.
     */
    @CallSuper
    public void release() {
      listener = null;
      bandwidthMeter = null;
    }
  
    /**
     * Called by the player to perform a track selection.
     *
     * @param rendererCapabilities The {@link RendererCapabilities} of the renderers for which tracks
     *     are to be selected.
     * @param trackGroups The available track groups.
     * @param periodId The {@link MediaPeriodId} of the period for which tracks are to be selected.
     * @param timeline The {@link Timeline} holding the period for which tracks are to be selected.
     * @return A {@link TrackSelectorResult} describing the track selections.
     * @throws ExoPlaybackException If an error occurs selecting tracks.
     */
    public abstract TrackSelectorResult selectTracks(
        RendererCapabilities[] rendererCapabilities,
        TrackGroupArray trackGroups,
        MediaPeriodId periodId,
        Timeline timeline)
        throws ExoPlaybackException;
  
    /**
     * Called by the player when a {@link TrackSelectorResult} previously generated by {@link
     * #selectTracks(RendererCapabilities[], TrackGroupArray, MediaPeriodId, Timeline)} is activated.
     *
     * @param info The value of {@link TrackSelectorResult#info} in the activated selection.
     */
    public abstract void onSelectionActivated(@Nullable Object info);
  
    /** Returns the current parameters for track selection. */
    public TrackSelectionParameters getParameters() {
      return TrackSelectionParameters.DEFAULT_WITHOUT_CONTEXT;
    }
  
    /**
     * Called by the player to provide parameters for track selection.
     *
     * <p>Only supported if {@link #isSetParametersSupported()} returns true.
     *
     * @param parameters The parameters for track selection.
     */
    public void setParameters(TrackSelectionParameters parameters) {
      // Default implementation doesn't support this method.
    }
  
    /**
     * Returns if this {@code TrackSelector} supports {@link
     * #setParameters(TrackSelectionParameters)}.
     *
     * <p>The same value is always returned for a given {@code TrackSelector} instance.
     */
    public boolean isSetParametersSupported() {
      return false;
    }
  
    /** Called by the player to set the {@link AudioAttributes} that will be used for playback. */
    public void setAudioAttributes(AudioAttributes audioAttributes) {
      // Default implementation is no-op.
    }
  
    /**
     * Calls {@link InvalidationListener#onTrackSelectionsInvalidated()} to invalidate all previously
     * generated track selections.
     */
    protected final void invalidate() {
      if (listener != null) {
        listener.onTrackSelectionsInvalidated();
      }
    }
  
    /**
     * Returns a bandwidth meter which can be used by track selections to select tracks. Must only be
     * called when the track selector is {@linkplain #init(InvalidationListener, BandwidthMeter)
     * initialized}.
     */
    protected final BandwidthMeter getBandwidthMeter() {
      return checkStateNotNull(bandwidthMeter);
    }
  }
  