Add a prototype OutputModifyingExtractor and use it in demo app to force every MP4 WebVTT sample to be a keyframe

demos/main/src/main/java/androidx/media3/demo/main/PlayerActivity.java

@@ -33,7 +33,9 @@ import androidx.appcompat.app.AppCompatActivity;
 import androidx.media3.common.AudioAttributes;
 import androidx.media3.common.C;
 import androidx.media3.common.ErrorMessageProvider;
+import androidx.media3.common.Format;
 import androidx.media3.common.MediaItem;
+import androidx.media3.common.MimeTypes;
 import androidx.media3.common.PlaybackException;
 import androidx.media3.common.Player;
 import androidx.media3.common.TrackSelectionParameters;
@@ -55,10 +57,15 @@ import androidx.media3.exoplayer.source.MediaSource;
 import androidx.media3.exoplayer.source.ads.AdsLoader;
 import androidx.media3.exoplayer.util.DebugTextViewHelper;
 import androidx.media3.exoplayer.util.EventLogger;
+import androidx.media3.extractor.DefaultExtractorsFactory;
+import androidx.media3.extractor.ForwardingTrackOutput;
+import androidx.media3.extractor.OutputModifyingExtractor;
+import androidx.media3.extractor.TrackOutput;
 import androidx.media3.ui.PlayerView;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Objects;
 import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 
 /** An activity that plays media using {@link ExoPlayer}. */
@@ -315,7 +322,10 @@ public class PlayerActivity extends AppCompatActivity
             serverSideAdsLoader,
             new DefaultMediaSourceFactory(/* context= */ this)
                 .setDataSourceFactory(dataSourceFactory));
-    return new DefaultMediaSourceFactory(/* context= */ this)
+    return new DefaultMediaSourceFactory(
+            /* context= */ this,
+            new OutputModifyingExtractor.Factory(
+                new DefaultExtractorsFactory(), Mp4VttKeyFrameTrackOutput::new))
         .setDataSourceFactory(dataSourceFactory)
         .setDrmSessionManagerProvider(drmSessionManagerProvider)
         .setLocalAdInsertionComponents(
@@ -323,6 +333,35 @@ public class PlayerActivity extends AppCompatActivity
         .setServerSideAdInsertionMediaSourceFactory(imaServerSideAdInsertionMediaSourceFactory);
   }
 
+  @OptIn(markerClass = UnstableApi.class)
+  private static final class Mp4VttKeyFrameTrackOutput extends ForwardingTrackOutput {
+
+    @Nullable private Format format;
+
+    public Mp4VttKeyFrameTrackOutput(TrackOutput trackOutput) {
+      super(trackOutput);
+    }
+
+    @Override
+    public void format(Format format) {
+      super.format(format);
+      this.format = format;
+    }
+
+    @Override
+    public void sampleMetadata(
+        long timeUs,
+        @C.BufferFlags int flags,
+        int size,
+        int offset,
+        @Nullable CryptoData cryptoData) {
+      if (format != null && Objects.equals(format.sampleMimeType, MimeTypes.APPLICATION_MP4VTT)) {
+        flags |= C.BUFFER_FLAG_KEY_FRAME;
+      }
+      super.sampleMetadata(timeUs, flags, size, offset, cryptoData);
+    }
+  }
+
   @OptIn(markerClass = UnstableApi.class)
   private void setRenderersFactory(
       ExoPlayer.Builder playerBuilder, boolean preferExtensionDecoders) {

libraries/extractor/src/main/java/androidx/media3/extractor/OutputModifyingExtractor.java

@@ -0,0 +1,149 @@
+/*
+ * Copyright 2024 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 androidx.media3.extractor;
+
+import android.net.Uri;
+import android.util.SparseArray;
+import androidx.annotation.Nullable;
+import androidx.media3.common.C;
+import androidx.media3.extractor.text.SubtitleParser;
+import com.google.common.base.Function;
+import java.io.IOException;
+import java.util.List;
+import java.util.Map;
+
+/** DO NOT SUBMIT document this and rename it */
+public final class OutputModifyingExtractor implements Extractor {
+
+  /**
+   * A wrapping {@link androidx.media3.extractor.ExtractorsFactory} implementation that wraps each
+   * returned {@link Extractor} instance with an {@link OutputModifyingExtractor}.
+   */
+  public static final class Factory implements ExtractorsFactory {
+
+    private final ExtractorsFactory delegate;
+    private final Function<TrackOutput, TrackOutput> wrappingTrackOutputFactory;
+
+    public Factory(
+        ExtractorsFactory delegate, Function<TrackOutput, TrackOutput> wrappingTrackOutputFactory) {
+      this.delegate = delegate;
+      this.wrappingTrackOutputFactory = wrappingTrackOutputFactory;
+    }
+
+    @Override
+    public ExtractorsFactory setSubtitleParserFactory(
+        SubtitleParser.Factory subtitleParserFactory) {
+      return delegate.setSubtitleParserFactory(subtitleParserFactory);
+    }
+
+    @Override
+    public Extractor[] createExtractors() {
+      return wrapExtractors(delegate.createExtractors());
+    }
+
+    @Override
+    public Extractor[] createExtractors(Uri uri, Map<String, List<String>> responseHeaders) {
+      return wrapExtractors(delegate.createExtractors(uri, responseHeaders));
+    }
+
+    private Extractor[] wrapExtractors(Extractor[] extractors) {
+      for (int i = 0; i < extractors.length; i++) {
+        extractors[i] = new OutputModifyingExtractor(extractors[i], wrappingTrackOutputFactory);
+      }
+      return extractors;
+    }
+  }
+
+  private final Extractor delegate;
+  private final Function<TrackOutput, TrackOutput> wrappingTrackOutputFactory;
+
+  public OutputModifyingExtractor(
+      Extractor delegate, Function<TrackOutput, TrackOutput> wrappingTrackOutputFactory) {
+    this.delegate = delegate;
+    this.wrappingTrackOutputFactory = wrappingTrackOutputFactory;
+  }
+
+  @Override
+  public boolean sniff(ExtractorInput input) throws IOException {
+    return delegate.sniff(input);
+  }
+
+  @Override
+  public void init(ExtractorOutput output) {
+    delegate.init(new WrappingExtractorOutput(output, wrappingTrackOutputFactory));
+  }
+
+  @Override
+  public @ReadResult int read(ExtractorInput input, PositionHolder seekPosition)
+      throws IOException {
+    return delegate.read(input, seekPosition);
+  }
+
+  @Override
+  public void seek(long position, long timeUs) {
+    delegate.seek(position, timeUs);
+  }
+
+  @Override
+  public List<SniffFailure> getSniffFailureDetails() {
+    return delegate.getSniffFailureDetails();
+  }
+
+  @Override
+  public Extractor getUnderlyingImplementation() {
+    return delegate.getUnderlyingImplementation();
+  }
+
+  @Override
+  public void release() {
+    delegate.release();
+  }
+
+  private static final class WrappingExtractorOutput implements ExtractorOutput {
+
+    private final ExtractorOutput delegateExtractorOutput;
+    private final Function<TrackOutput, TrackOutput> wrappingTrackOutputFactory;
+    private final SparseArray<TrackOutput> trackOutputs;
+
+    private WrappingExtractorOutput(
+        ExtractorOutput delegateExtractorOutput,
+        Function<TrackOutput, TrackOutput> wrappingTrackOutputFactory) {
+      this.delegateExtractorOutput = delegateExtractorOutput;
+      this.wrappingTrackOutputFactory = wrappingTrackOutputFactory;
+      trackOutputs = new SparseArray<>();
+    }
+
+    @Override
+    public TrackOutput track(int id, @C.TrackType int type) {
+      @Nullable TrackOutput trackOutput = trackOutputs.get(id);
+      if (trackOutput == null) {
+        trackOutput = wrappingTrackOutputFactory.apply(delegateExtractorOutput.track(id, type));
+        trackOutputs.put(id, trackOutput);
+      }
+      return trackOutput;
+    }
+
+    @Override
+    public void endTracks() {
+      delegateExtractorOutput.endTracks();
+    }
+
+    @Override
+    public void seekMap(SeekMap seekMap) {
+      delegateExtractorOutput.seekMap(seekMap);
+    }
+  }
+}