Introduce MetadataDecoderFactory

This is analogous to what we do for text/subtitles, and
adds support for playlists where the type of metadata
changes from one playlist item to the next.

Issue: #2176

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=143948307

demo/src/main/java/com/google/android/exoplayer2/demo/PlayerActivity.java

@@ -278,7 +278,7 @@ public class PlayerActivity extends Activity implements OnClickListener, ExoPlay
       player.addListener(eventLogger);
       player.setAudioDebugListener(eventLogger);
       player.setVideoDebugListener(eventLogger);
-      player.setId3Output(eventLogger);
+      player.setMetadataOutput(eventLogger);
 
       simpleExoPlayerView.setPlayer(player);
       if (isTimelineStatic) {

library/src/main/java/com/google/android/exoplayer2/SimpleExoPlayer.java

@@ -36,7 +36,6 @@ import com.google.android.exoplayer2.drm.FrameworkMediaCrypto;
 import com.google.android.exoplayer2.mediacodec.MediaCodecSelector;
 import com.google.android.exoplayer2.metadata.Metadata;
 import com.google.android.exoplayer2.metadata.MetadataRenderer;
-import com.google.android.exoplayer2.metadata.id3.Id3Decoder;
 import com.google.android.exoplayer2.source.MediaSource;
 import com.google.android.exoplayer2.source.TrackGroupArray;
 import com.google.android.exoplayer2.text.Cue;
@@ -448,15 +447,6 @@ public class SimpleExoPlayer implements ExoPlayer {
     textOutput = output;
   }
 
-  /**
-   * @deprecated Use {@link #setMetadataOutput(MetadataRenderer.Output)} instead.
-   * @param output The output.
-   */
-  @Deprecated
-  public void setId3Output(MetadataRenderer.Output output) {
-    setMetadataOutput(output);
-  }
-
   /**
    * Sets a listener to receive metadata events.
    *
@@ -771,7 +761,7 @@ public class SimpleExoPlayer implements ExoPlayer {
   protected void buildMetadataRenderers(Context context, Handler mainHandler,
       @ExtensionRendererMode int extensionRendererMode, MetadataRenderer.Output output,
       ArrayList<Renderer> out) {
-    out.add(new MetadataRenderer(output, mainHandler.getLooper(), new Id3Decoder()));
+    out.add(new MetadataRenderer(output, mainHandler.getLooper()));
   }
 
   /**

library/src/main/java/com/google/android/exoplayer2/metadata/MetadataDecoderFactory.java

@@ -0,0 +1,99 @@
+/*
+ * 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.metadata;
+
+import com.google.android.exoplayer2.Format;
+import com.google.android.exoplayer2.metadata.emsg.EventMessageDecoder;
+import com.google.android.exoplayer2.metadata.id3.Id3Decoder;
+import com.google.android.exoplayer2.metadata.scte35.SpliceInfoDecoder;
+import com.google.android.exoplayer2.util.MimeTypes;
+
+/**
+ * A factory for {@link MetadataDecoder} instances.
+ */
+public interface MetadataDecoderFactory {
+
+  /**
+   * Returns whether the factory is able to instantiate a {@link MetadataDecoder} for the given
+   * {@link Format}.
+   *
+   * @param format The {@link Format}.
+   * @return Whether the factory can instantiate a suitable {@link MetadataDecoder}.
+   */
+  boolean supportsFormat(Format format);
+
+  /**
+   * Creates a {@link MetadataDecoder} for the given {@link Format}.
+   *
+   * @param format The {@link Format}.
+   * @return A new {@link MetadataDecoder}.
+   * @throws IllegalArgumentException If the {@link Format} is not supported.
+   */
+  MetadataDecoder createDecoder(Format format);
+
+  /**
+   * Default {@link MetadataDecoder} implementation.
+   * <p>
+   * The formats supported by this factory are:
+   * <ul>
+   * <li>ID3 ({@link Id3Decoder})</li>
+   * <li>EMSG ({@link EventMessageDecoder})</li>
+   * <li>SCTE-35 ({@link SpliceInfoDecoder})</li>
+   * </ul>
+   */
+  MetadataDecoderFactory DEFAULT = new MetadataDecoderFactory() {
+
+    @Override
+    public boolean supportsFormat(Format format) {
+      return getDecoderClass(format.sampleMimeType) != null;
+    }
+
+    @Override
+    public MetadataDecoder createDecoder(Format format) {
+      try {
+        Class<?> clazz = getDecoderClass(format.sampleMimeType);
+        if (clazz == null) {
+          throw new IllegalArgumentException("Attempted to create decoder for unsupported format");
+        }
+        return clazz.asSubclass(MetadataDecoder.class).getConstructor().newInstance();
+      } catch (Exception e) {
+        throw new IllegalStateException("Unexpected error instantiating decoder", e);
+      }
+    }
+
+    private Class<?> getDecoderClass(String mimeType) {
+      if (mimeType == null) {
+        return null;
+      }
+      try {
+        switch (mimeType) {
+          case MimeTypes.APPLICATION_ID3:
+            return Class.forName("com.google.android.exoplayer2.metadata.id3.Id3Decoder");
+          case MimeTypes.APPLICATION_EMSG:
+            return Class.forName("com.google.android.exoplayer2.metadata.emsg.EventMessageDecoder");
+          case MimeTypes.APPLICATION_SCTE35:
+            return Class.forName("com.google.android.exoplayer2.metadata.scte35.SpliceInfoDecoder");
+          default:
+            return null;
+        }
+      } catch (ClassNotFoundException e) {
+        return null;
+      }
+    }
+
+  };
+
+}

library/src/main/java/com/google/android/exoplayer2/metadata/MetadataRenderer.java

@@ -49,12 +49,13 @@ public final class MetadataRenderer extends BaseRenderer implements Callback {
 
   private static final int MSG_INVOKE_RENDERER = 0;
 
-  private final MetadataDecoder metadataDecoder;
+  private final MetadataDecoderFactory decoderFactory;
   private final Output output;
   private final Handler outputHandler;
   private final FormatHolder formatHolder;
   private final DecoderInputBuffer buffer;
 
+  private MetadataDecoder decoder;
   private boolean inputStreamEnded;
   private long pendingMetadataTimestamp;
   private Metadata pendingMetadata;
@@ -66,21 +67,38 @@ public final class MetadataRenderer extends BaseRenderer implements Callback {
    *     looper associated with the application's main thread, which can be obtained using
    *     {@link android.app.Activity#getMainLooper()}. Null may be passed if the output should be
    *     called directly on the player's internal rendering thread.
-   * @param metadataDecoder A decoder for the metadata.
    */
-  public MetadataRenderer(Output output, Looper outputLooper, MetadataDecoder metadataDecoder) {
+  public MetadataRenderer(Output output, Looper outputLooper) {
+    this(output, outputLooper, MetadataDecoderFactory.DEFAULT);
+  }
+
+  /**
+   * @param output The output.
+   * @param outputLooper The looper associated with the thread on which the output should be called.
+   *     If the output makes use of standard Android UI components, then this should normally be the
+   *     looper associated with the application's main thread, which can be obtained using
+   *     {@link android.app.Activity#getMainLooper()}. Null may be passed if the output should be
+   *     called directly on the player's internal rendering thread.
+   * @param decoderFactory A factory from which to obtain {@link MetadataDecoder} instances.
+   */
+  public MetadataRenderer(Output output, Looper outputLooper,
+      MetadataDecoderFactory decoderFactory) {
     super(C.TRACK_TYPE_METADATA);
     this.output = Assertions.checkNotNull(output);
     this.outputHandler = outputLooper == null ? null : new Handler(outputLooper, this);
-    this.metadataDecoder = Assertions.checkNotNull(metadataDecoder);
+    this.decoderFactory = Assertions.checkNotNull(decoderFactory);
     formatHolder = new FormatHolder();
     buffer = new DecoderInputBuffer(DecoderInputBuffer.BUFFER_REPLACEMENT_MODE_NORMAL);
   }
 
   @Override
   public int supportsFormat(Format format) {
-    return metadataDecoder.canDecode(format.sampleMimeType) ? FORMAT_HANDLED
+    return decoderFactory.supportsFormat(format) ? FORMAT_HANDLED : FORMAT_UNSUPPORTED_TYPE;
-        : FORMAT_UNSUPPORTED_TYPE;
+  }
+
+  @Override
+  protected void onStreamChanged(Format[] formats) throws ExoPlaybackException {
+    decoder = decoderFactory.createDecoder(formats[0]);
   }
 
   @Override
@@ -102,7 +120,7 @@ public final class MetadataRenderer extends BaseRenderer implements Callback {
           try {
             buffer.flip();
             ByteBuffer bufferData = buffer.data;
-            pendingMetadata = metadataDecoder.decode(bufferData.array(), bufferData.limit());
+            pendingMetadata = decoder.decode(bufferData.array(), bufferData.limit());
           } catch (MetadataDecoderException e) {
             throw ExoPlaybackException.createForRenderer(e, getIndex());
           }
@@ -119,6 +137,7 @@ public final class MetadataRenderer extends BaseRenderer implements Callback {
   @Override
   protected void onDisabled() {
     pendingMetadata = null;
+    decoder = null;
     super.onDisabled();
   }