Add an AC3 bitstream extractor

Defined in ATSC Standard: Digital Audio Compression (AC-3, E-AC-3).
Link: http://atsc.org/wp-content/uploads/2015/03/A52-201212-17.pdf.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=131294260

library/src/androidTest/assets/ts/sample.ac3.0.dump

@@ -0,0 +1,61 @@
+seekMap:
+  isSeekable = false
+  duration = UNSET TIME
+  getPosition(0) = 0
+numberOfTracks = 1
+track 0:
+  format:
+    bitrate = -1
+    id = null
+    containerMimeType = null
+    sampleMimeType = audio/ac3
+    maxInputSize = -1
+    width = -1
+    height = -1
+    frameRate = -1.0
+    rotationDegrees = -1
+    pixelWidthHeightRatio = -1.0
+    channelCount = 6
+    sampleRate = 48000
+    pcmEncoding = -1
+    encoderDelay = -1
+    encoderPadding = -1
+    subsampleOffsetUs = 9223372036854775807
+    selectionFlags = 0
+    language = null
+    drmInitData = -
+    initializationData:
+  sample count = 8
+  sample 0:
+    time = 0
+    flags = 1
+    data = length 1536, hash 7108D5C2
+  sample 1:
+    time = 32000
+    flags = 1
+    data = length 1536, hash 80BF3B34
+  sample 2:
+    time = 64000
+    flags = 1
+    data = length 1536, hash 5D09685
+  sample 3:
+    time = 96000
+    flags = 1
+    data = length 1536, hash A9A24E44
+  sample 4:
+    time = 128000
+    flags = 1
+    data = length 1536, hash 6F856273
+  sample 5:
+    time = 160000
+    flags = 1
+    data = length 1536, hash B1737D3C
+  sample 6:
+    time = 192000
+    flags = 1
+    data = length 1536, hash 98FDEB9D
+  sample 7:
+    time = 224000
+    flags = 1
+    data = length 1536, hash 99B9B943
+tracksEnded = true

library/src/androidTest/java/com/google/android/exoplayer2/extractor/ts/Ac3ExtractorTest.java

@@ -0,0 +1,36 @@
+/*
+ * 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.extractor.ts;
+
+import android.test.InstrumentationTestCase;
+import com.google.android.exoplayer2.extractor.Extractor;
+import com.google.android.exoplayer2.testutil.TestUtil;
+
+/**
+ * Unit test for {@link Ac3Extractor}.
+ */
+public final class Ac3ExtractorTest extends InstrumentationTestCase {
+
+  public void testSample() throws Exception {
+    TestUtil.assertOutput(new TestUtil.ExtractorFactory() {
+      @Override
+      public Extractor create() {
+        return new Ac3Extractor();
+      }
+    }, "ts/sample.ac3", getInstrumentation());
+  }
+
+}

library/src/main/java/com/google/android/exoplayer2/extractor/DefaultExtractorsFactory.java

@@ -87,6 +87,13 @@ public final class DefaultExtractorsFactory implements ExtractorsFactory {
         } catch (ClassNotFoundException e) {
           // Extractor not found.
         }
+        try {
+          extractorClasses.add(
+              Class.forName("com.google.android.exoplayer2.extractor.ts.Ac3Extractor")
+                  .asSubclass(Extractor.class));
+        } catch (ClassNotFoundException e) {
+          // Extractor not found.
+        }
         try {
           extractorClasses.add(
               Class.forName("com.google.android.exoplayer2.extractor.ts.TsExtractor")

library/src/main/java/com/google/android/exoplayer2/extractor/ts/Ac3Extractor.java

@@ -0,0 +1,156 @@
+/*
+ * 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.extractor.ts;
+
+import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.audio.Ac3Util;
+import com.google.android.exoplayer2.extractor.Extractor;
+import com.google.android.exoplayer2.extractor.ExtractorInput;
+import com.google.android.exoplayer2.extractor.ExtractorOutput;
+import com.google.android.exoplayer2.extractor.ExtractorsFactory;
+import com.google.android.exoplayer2.extractor.PositionHolder;
+import com.google.android.exoplayer2.extractor.SeekMap;
+import com.google.android.exoplayer2.util.ParsableByteArray;
+import com.google.android.exoplayer2.util.Util;
+
+import java.io.IOException;
+
+/**
+ * Facilitates the extraction of AC-3 samples from elementary audio files formatted as AC-3
+ * bitstreams.
+ */
+public final class Ac3Extractor implements Extractor {
+
+  /**
+   * Factory for {@link Ac3Extractor} instances.
+   */
+  public static final ExtractorsFactory FACTORY = new ExtractorsFactory() {
+
+    @Override
+    public Extractor[] createExtractors() {
+      return new Extractor[] {new Ac3Extractor()};
+    }
+
+  };
+
+  /**
+   * The maximum number of bytes to search when sniffing, excluding ID3 information, before giving
+   * up.
+   */
+  private static final int MAX_SNIFF_BYTES = 8 * 1024;
+  private static final int AC3_SYNC_WORD = 0x0B77;
+  private static final int MAX_SYNC_FRAME_SIZE = 2786;
+  private static final int ID3_TAG = Util.getIntegerCodeForString("ID3");
+
+  private final long firstSampleTimestampUs;
+  private final ParsableByteArray sampleData;
+
+  private Ac3Reader reader;
+  private boolean startedPacket;
+
+  public Ac3Extractor() {
+    this(0);
+  }
+
+  public Ac3Extractor(long firstSampleTimestampUs) {
+    this.firstSampleTimestampUs = firstSampleTimestampUs;
+    sampleData = new ParsableByteArray(MAX_SYNC_FRAME_SIZE);
+  }
+
+  @Override
+  public boolean sniff(ExtractorInput input) throws IOException, InterruptedException {
+    // Skip any ID3 headers.
+    ParsableByteArray scratch = new ParsableByteArray(10);
+    int startPosition = 0;
+    while (true) {
+      input.peekFully(scratch.data, 0, 10);
+      scratch.setPosition(0);
+      if (scratch.readUnsignedInt24() != ID3_TAG) {
+        break;
+      }
+      scratch.skipBytes(3);
+      int length = scratch.readSynchSafeInt();
+      startPosition += 10 + length;
+      input.advancePeekPosition(length);
+    }
+    input.resetPeekPosition();
+    input.advancePeekPosition(startPosition);
+
+    int headerPosition = startPosition;
+    int validFramesCount = 0;
+    while (true) {
+      input.peekFully(scratch.data, 0, 5);
+      scratch.setPosition(0);
+      int syncBytes = scratch.readUnsignedShort();
+      if (syncBytes != AC3_SYNC_WORD) {
+        validFramesCount = 0;
+        input.resetPeekPosition();
+        if (++headerPosition - startPosition >= MAX_SNIFF_BYTES) {
+          return false;
+        }
+        input.advancePeekPosition(headerPosition);
+      } else {
+        if (++validFramesCount >= 4) {
+          return true;
+        }
+        int frameSize = Ac3Util.parseAc3SyncframeSize(scratch.data);
+        input.advancePeekPosition(frameSize - 5);
+      }
+    }
+  }
+
+  @Override
+  public void init(ExtractorOutput output) {
+    reader = new Ac3Reader(output.track(0), false); // TODO: Add support for embedded ID3.
+    output.endTracks();
+    output.seekMap(new SeekMap.Unseekable(C.TIME_UNSET));
+  }
+
+  @Override
+  public void seek(long position) {
+    startedPacket = false;
+    reader.seek();
+  }
+
+  @Override
+  public void release() {
+    // Do nothing.
+  }
+
+  @Override
+  public int read(ExtractorInput input, PositionHolder seekPosition) throws IOException,
+      InterruptedException {
+    int bytesRead = input.read(sampleData.data, 0, MAX_SYNC_FRAME_SIZE);
+    if (bytesRead == C.RESULT_END_OF_INPUT) {
+      return RESULT_END_OF_INPUT;
+    }
+
+    // Feed whatever data we have to the reader, regardless of whether the read finished or not.
+    sampleData.setPosition(0);
+    sampleData.setLimit(bytesRead);
+
+    if (!startedPacket) {
+      // Pass data to the reader as though it's contained within a single infinitely long packet.
+      reader.packetStarted(firstSampleTimestampUs, true);
+      startedPacket = true;
+    }
+    // TODO: Make it possible for the reader to consume the dataSource directly, so that it becomes
+    // unnecessary to copy the data through packetBuffer.
+    reader.consume(sampleData);
+    return RESULT_CONTINUE;
+  }
+
+}

library/src/main/java/com/google/android/exoplayer2/extractor/ts/Ac3Reader.java

@@ -51,6 +51,7 @@ import com.google.android.exoplayer2.util.ParsableByteArray;
   // Used when reading the samples.
   private long timeUs;
 
+  // TODO: Remove the isEac3 parameter by reading the BSID field.
   /**
    * Constructs a new reader for (E-)AC-3 elementary streams.
    *

library/src/main/java/com/google/android/exoplayer2/extractor/ts/AdtsExtractor.java

@@ -57,7 +57,7 @@ public final class AdtsExtractor implements Extractor {
   private final ParsableByteArray packetBuffer;
 
   // Accessed only by the loading thread.
-  private AdtsReader adtsReader;
+  private AdtsReader reader;
   private boolean startedPacket;
 
   public AdtsExtractor() {
@@ -81,8 +81,8 @@ public final class AdtsExtractor implements Extractor {
       if (scratch.readUnsignedInt24() != ID3_TAG) {
         break;
       }
-      int length = (scratch.data[6] & 0x7F) << 21 | ((scratch.data[7] & 0x7F) << 14)
-          | ((scratch.data[8] & 0x7F) << 7) | (scratch.data[9] & 0x7F);
+      scratch.skipBytes(3);
+      int length = scratch.readSynchSafeInt();
       startPosition += 10 + length;
       input.advancePeekPosition(length);
     }
@@ -126,7 +126,7 @@ public final class AdtsExtractor implements Extractor {
 
   @Override
   public void init(ExtractorOutput output) {
-    adtsReader = new AdtsReader(output.track(0), output.track(1));
+    reader = new AdtsReader(output.track(0), output.track(1));
     output.endTracks();
     output.seekMap(new SeekMap.Unseekable(C.TIME_UNSET));
   }
@@ -134,7 +134,7 @@ public final class AdtsExtractor implements Extractor {
   @Override
   public void seek(long position) {
     startedPacket = false;
-    adtsReader.seek();
+    reader.seek();
   }
 
   @Override
@@ -154,14 +154,14 @@ public final class AdtsExtractor implements Extractor {
     packetBuffer.setPosition(0);
     packetBuffer.setLimit(bytesRead);
 
-    // TODO: Make it possible for adtsReader to consume the dataSource directly, so that it becomes
-    // unnecessary to copy the data through packetBuffer.
     if (!startedPacket) {
       // Pass data to the reader as though it's contained within a single infinitely long packet.
-      adtsReader.packetStarted(firstSampleTimestampUs, true);
+      reader.packetStarted(firstSampleTimestampUs, true);
       startedPacket = true;
     }
-    adtsReader.consume(packetBuffer);
+    // TODO: Make it possible for reader to consume the dataSource directly, so that it becomes
+    // unnecessary to copy the data through packetBuffer.
+    reader.consume(packetBuffer);
     return RESULT_CONTINUE;
   }