Use a MediaSource factory internally in AdsMediaSource

Support ad MediaSources that aren't prepared immediately by using
DeferredMediaPeriod, moved up from DynamicConcatenatingMediaSource.

In a later change the new interfaces will be made public so that apps
can provide their own MediaSource factories.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=177424172

library/core/src/main/java/com/google/android/exoplayer2/source/DeferredMediaPeriod.java

+/*
+ * Copyright (C) 2017 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.source;
+
+import com.google.android.exoplayer2.source.MediaSource.MediaPeriodId;
+import com.google.android.exoplayer2.trackselection.TrackSelection;
+import com.google.android.exoplayer2.upstream.Allocator;
+import java.io.IOException;
+
+/**
+ * Media period that wraps a media source and defers calling its
+ * {@link MediaSource#createPeriod(MediaPeriodId, Allocator)} method until {@link #createPeriod()}
+ * has been called. This is useful if you need to return a media period immediately but the media
+ * source that should create it is not yet prepared.
+ */
+public final class DeferredMediaPeriod implements MediaPeriod, MediaPeriod.Callback {
+
+  public final MediaSource mediaSource;
+
+  private final MediaPeriodId id;
+  private final Allocator allocator;
+
+  private MediaPeriod mediaPeriod;
+  private Callback callback;
+  private long preparePositionUs;
+
+  public DeferredMediaPeriod(MediaSource mediaSource, MediaPeriodId id, Allocator allocator) {
+    this.id = id;
+    this.allocator = allocator;
+    this.mediaSource = mediaSource;
+  }
+
+  /**
+   * Calls {@link MediaSource#createPeriod(MediaPeriodId, Allocator)} on the wrapped source then
+   * prepares it if {@link #prepare(Callback, long)} has been called. Call {@link #releasePeriod()}
+   * to release the period.
+   */
+  public void createPeriod() {
+    mediaPeriod = mediaSource.createPeriod(id, allocator);
+    if (callback != null) {
+      mediaPeriod.prepare(this, preparePositionUs);
+    }
+  }
+
+  /**
+   * Releases the period.
+   */
+  public void releasePeriod() {
+    if (mediaPeriod != null) {
+      mediaSource.releasePeriod(mediaPeriod);
+    }
+  }
+
+  @Override
+  public void prepare(Callback callback, long preparePositionUs) {
+    this.callback = callback;
+    this.preparePositionUs = preparePositionUs;
+    if (mediaPeriod != null) {
+      mediaPeriod.prepare(this, preparePositionUs);
+    }
+  }
+
+  @Override
+  public void maybeThrowPrepareError() throws IOException {
+    if (mediaPeriod != null) {
+      mediaPeriod.maybeThrowPrepareError();
+    } else {
+      mediaSource.maybeThrowSourceInfoRefreshError();
+    }
+  }
+
+  @Override
+  public TrackGroupArray getTrackGroups() {
+    return mediaPeriod.getTrackGroups();
+  }
+
+  @Override
+  public long selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
+      SampleStream[] streams, boolean[] streamResetFlags, long positionUs) {
+    return mediaPeriod.selectTracks(selections, mayRetainStreamFlags, streams, streamResetFlags,
+        positionUs);
+  }
+
+  @Override
+  public void discardBuffer(long positionUs, boolean toKeyframe) {
+    mediaPeriod.discardBuffer(positionUs, toKeyframe);
+  }
+
+  @Override
+  public long readDiscontinuity() {
+    return mediaPeriod.readDiscontinuity();
+  }
+
+  @Override
+  public long getBufferedPositionUs() {
+    return mediaPeriod.getBufferedPositionUs();
+  }
+
+  @Override
+  public long seekToUs(long positionUs) {
+    return mediaPeriod.seekToUs(positionUs);
+  }
+
+  @Override
+  public long getNextLoadPositionUs() {
+    return mediaPeriod.getNextLoadPositionUs();
+  }
+
+  @Override
+  public boolean continueLoading(long positionUs) {
+    return mediaPeriod != null && mediaPeriod.continueLoading(positionUs);
+  }
+
+  @Override
+  public void onContinueLoadingRequested(MediaPeriod source) {
+    callback.onContinueLoadingRequested(this);
+  }
+
+  // MediaPeriod.Callback implementation
+
+  @Override
+  public void onPrepared(MediaPeriod mediaPeriod) {
+    callback.onPrepared(this);
+  }
+
+}

library/core/src/main/java/com/google/android/exoplayer2/source/DynamicConcatenatingMediaSource.java

@@ -27,7 +27,6 @@ import com.google.android.exoplayer2.ExoPlayer.ExoPlayerComponent;
 import com.google.android.exoplayer2.ExoPlayer.ExoPlayerMessage;
 import com.google.android.exoplayer2.ExoPlayer.ExoPlayerMessage;
 import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.source.ShuffleOrder.DefaultShuffleOrder;
 import com.google.android.exoplayer2.source.ShuffleOrder.DefaultShuffleOrder;
-import com.google.android.exoplayer2.trackselection.TrackSelection;
 import com.google.android.exoplayer2.upstream.Allocator;
 import com.google.android.exoplayer2.upstream.Allocator;
 import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.Util;
 import com.google.android.exoplayer2.util.Util;
@@ -758,111 +757,5 @@ public final class DynamicConcatenatingMediaSource implements MediaSource, ExoPl
 
 
   }
   }
 
 
-  /**
-   * Media period used for periods created from unprepared media sources exposed through
-   * {@link DeferredTimeline}. Period preparation is postponed until the actual media source becomes
-   * available.
-   */
-  private static final class DeferredMediaPeriod implements MediaPeriod, MediaPeriod.Callback {
-
-    public final MediaSource mediaSource;
-
-    private final MediaPeriodId id;
-    private final Allocator allocator;
-
-    private MediaPeriod mediaPeriod;
-    private Callback callback;
-    private long preparePositionUs;
-
-    public DeferredMediaPeriod(MediaSource mediaSource, MediaPeriodId id, Allocator allocator) {
-      this.id = id;
-      this.allocator = allocator;
-      this.mediaSource = mediaSource;
-    }
-
-    public void createPeriod() {
-      mediaPeriod = mediaSource.createPeriod(id, allocator);
-      if (callback != null) {
-        mediaPeriod.prepare(this, preparePositionUs);
-      }
-    }
-
-    public void releasePeriod() {
-      if (mediaPeriod != null) {
-        mediaSource.releasePeriod(mediaPeriod);
-      }
-    }
-
-    @Override
-    public void prepare(Callback callback, long preparePositionUs) {
-      this.callback = callback;
-      this.preparePositionUs = preparePositionUs;
-      if (mediaPeriod != null) {
-        mediaPeriod.prepare(this, preparePositionUs);
-      }
-    }
-
-    @Override
-    public void maybeThrowPrepareError() throws IOException {
-      if (mediaPeriod != null) {
-        mediaPeriod.maybeThrowPrepareError();
-      } else {
-        mediaSource.maybeThrowSourceInfoRefreshError();
-      }
-    }
-
-    @Override
-    public TrackGroupArray getTrackGroups() {
-      return mediaPeriod.getTrackGroups();
-    }
-
-    @Override
-    public long selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
-        SampleStream[] streams, boolean[] streamResetFlags, long positionUs) {
-      return mediaPeriod.selectTracks(selections, mayRetainStreamFlags, streams, streamResetFlags,
-          positionUs);
-    }
-
-    @Override
-    public void discardBuffer(long positionUs, boolean toKeyframe) {
-      mediaPeriod.discardBuffer(positionUs, toKeyframe);
-    }
-
-    @Override
-    public long readDiscontinuity() {
-      return mediaPeriod.readDiscontinuity();
-    }
-
-    @Override
-    public long getBufferedPositionUs() {
-      return mediaPeriod.getBufferedPositionUs();
-    }
-
-    @Override
-    public long seekToUs(long positionUs) {
-      return mediaPeriod.seekToUs(positionUs);
-    }
-
-    @Override
-    public long getNextLoadPositionUs() {
-      return mediaPeriod.getNextLoadPositionUs();
-    }
-
-    @Override
-    public boolean continueLoading(long positionUs) {
-      return mediaPeriod != null && mediaPeriod.continueLoading(positionUs);
-    }
-
-    @Override
-    public void onContinueLoadingRequested(MediaPeriod source) {
-      callback.onContinueLoadingRequested(this);
-    }
-
-    @Override
-    public void onPrepared(MediaPeriod mediaPeriod) {
-      callback.onPrepared(this);
-    }
-  }
-
 }
 }