Add AC-4 format support

* Add AC-4 MIME type definition
 * Add AC-4 format support in Mp4Extractor and TsExtractor
 * Add AC-4 Extractor
 * Add AC-4 playback support in MPEG-4, MPEG-DASH, TS and HLS

library/core/src/main/java/com/google/android/exoplayer2/C.java

@@ -143,8 +143,8 @@ public final class C {
    * {@link #ENCODING_INVALID}, {@link #ENCODING_PCM_8BIT}, {@link #ENCODING_PCM_16BIT}, {@link
    * #ENCODING_PCM_24BIT}, {@link #ENCODING_PCM_32BIT}, {@link #ENCODING_PCM_FLOAT}, {@link
    * #ENCODING_PCM_MU_LAW}, {@link #ENCODING_PCM_A_LAW}, {@link #ENCODING_AC3}, {@link
-   * #ENCODING_E_AC3}, {@link #ENCODING_DTS}, {@link #ENCODING_DTS_HD} or {@link
+   * #ENCODING_E_AC3}, {@link #ENCODING_DTS}, {@link #ENCODING_DTS_HD}, {@link
-   * #ENCODING_DOLBY_TRUEHD}.
+   * #ENCODING_DOLBY_TRUEHD} or {@link #ENCODING_AC4}.
    */
   @Documented
   @Retention(RetentionPolicy.SOURCE)
@@ -162,7 +162,8 @@ public final class C {
     ENCODING_E_AC3,
     ENCODING_DTS,
     ENCODING_DTS_HD,
-    ENCODING_DOLBY_TRUEHD
+    ENCODING_DOLBY_TRUEHD,
+    ENCODING_AC4
   })
   public @interface Encoding {}
 
@@ -212,6 +213,8 @@ public final class C {
   public static final int ENCODING_DTS_HD = AudioFormat.ENCODING_DTS_HD;
   /** @see AudioFormat#ENCODING_DOLBY_TRUEHD */
   public static final int ENCODING_DOLBY_TRUEHD = AudioFormat.ENCODING_DOLBY_TRUEHD;
+  /** @see AudioFormat#ENCODING_AC4 */
+  public static final int ENCODING_AC4 = AudioFormat.ENCODING_AC4;
 
   /**
    * Stream types for an {@link android.media.AudioTrack}. One of {@link #STREAM_TYPE_ALARM}, {@link

library/core/src/main/java/com/google/android/exoplayer2/audio/Ac4Util.java

@@ -0,0 +1,269 @@
+/*
+ * Copyright (C) 2018 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.audio;
+
+import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.Format;
+import com.google.android.exoplayer2.drm.DrmInitData;
+import com.google.android.exoplayer2.util.MimeTypes;
+import com.google.android.exoplayer2.util.ParsableBitArray;
+import com.google.android.exoplayer2.util.ParsableByteArray;
+import java.nio.ByteBuffer;
+
+/**
+ * Utility methods for parsing AC-4 frames, which are access units in AC-4 bitstreams.
+ */
+public final class Ac4Util {
+
+  /**
+   * Holds sample format information as presented by a syncframe header.
+   */
+  public static final class SyncFrameInfo {
+
+    /**
+     * The sample mime type of the bitstream is {@link MimeTypes#AUDIO_AC4}.
+     */
+    public final String mimeType;
+    /**
+     * The bitstream version.
+     */
+    public final int bitstreamVersion;
+    /**
+     * The audio sampling rate in Hz.
+     */
+    public final int sampleRate;
+    /**
+     * The number of audio channels
+     */
+    public final int channelCount;
+    /**
+     * The size of the frame.
+     */
+    public final int frameSize;
+    /**
+     * Number of audio samples in the frame.
+     */
+    public final int sampleCount;
+
+    private SyncFrameInfo(
+        String mimeType,
+        int bitstreamVersion,
+        int channelCount,
+        int sampleRate,
+        int frameSize,
+        int sampleCount) {
+      this.mimeType = mimeType;
+      this.bitstreamVersion = bitstreamVersion;
+      this.channelCount = channelCount;
+      this.sampleRate = sampleRate;
+      this.frameSize = frameSize;
+      this.sampleCount = sampleCount;
+    }
+  }
+
+  /**
+   * The channel count of AC-4 stream.
+   */
+  // TODO: Parse AC-4 stream channel count.
+  public static final int CHANNEL_COUNT_2 = 2;
+  /**
+   * The header size for AC-4 parser. Only needs to be as big as we need to read, not the full
+   * header size.
+   */
+  public static final int HEADER_SIZE_FOR_PARSER = 16;
+  /**
+   * Number of audio samples in the frame. Defined in IEC61937-14:2017 table 5 and 6. This table
+   * provides the number of samples per frame at the playback sampling frequency of 48kHz. For
+   * 44.1kHz, only frame_rate_index(13) is valid and corresponding sample count is 2048.
+   */
+  private static final int[] SAMPLE_COUNT = new int[] {
+      /* [ 0]  23.976 fps */ 2002,
+      /* [ 1]  24     fps */ 2000,
+      /* [ 2]  25     fps */ 1920,
+      /* [ 3]  29.97  fps */ 1601,  // 1601 | 1602 | 1601 | 1602 | 1602
+      /* [ 4]  30     fps */ 1600,
+      /* [ 5]  47.95  fps */ 1001,
+      /* [ 6]  48     fps */ 1000,
+      /* [ 7]  50     fps */  960,
+      /* [ 8]  59.94  fps */  800,  //  800 |  801 |  801 |  801 |  801
+      /* [ 9]  60     fps */  800,
+      /* [10] 100     fps */  480,
+      /* [11] 119.88  fps */  400,  //  400 |  400 |  401 |  400 |  401
+      /* [12] 120     fps */  400,
+      /* [13]  23.438 fps */ 2048
+  };
+
+  /**
+   * Returns the AC-4 format given {@code data} containing the AC4SpecificBox according to ETSI TS
+   * 103 190-1 Annex E. The reading position of {@code data} will be modified.
+   *
+   * @param data The AC4SpecificBox to parse.
+   * @param trackId The track identifier to set on the format.
+   * @param language The language to set on the format.
+   * @param drmInitData {@link DrmInitData} to be included in the format.
+   * @return The AC-4 format parsed from data in the header.
+   */
+  public static Format parseAc4AnnexEFormat(
+      ParsableByteArray data, String trackId, String language, DrmInitData drmInitData) {
+    data.skipBytes(1);
+    int sampleRate = ((data.readUnsignedByte() & 0x20) >> 5 == 1) ? 48000 : 44100;
+    return Format.createAudioSampleFormat(
+        trackId,
+        MimeTypes.AUDIO_AC4,
+        null,
+        Format.NO_VALUE,
+        Format.NO_VALUE,
+        CHANNEL_COUNT_2,
+        sampleRate,
+        null,
+        drmInitData,
+        0,
+        language);
+  }
+
+  private static int readVariableBits(ParsableBitArray data, int nbits) {
+    int value = 0;
+    while (true) {
+      int moreBits;
+      value += data.readBits(nbits);
+      moreBits = data.readBits(1);
+      if (moreBits == 0)
+        break;
+      value++;
+      value <<= nbits;
+    }
+    return value;
+  }
+
+  /**
+   * Returns AC-4 format information given {@code data} containing a syncframe. The reading
+   * position of {@code data} will be modified.
+   *
+   * @param data The data to parse, positioned at the start of the syncframe.
+   * @return The AC-4 format data parsed from the header.
+   */
+  public static SyncFrameInfo parseAc4SyncframeInfo(ParsableBitArray data) {
+    int headerSize = 0;
+    int syncWord  = data.readBits(16);
+    headerSize += 2;
+    int frameSize = data.readBits(16);
+    headerSize += 2;
+    if (frameSize == 0xFFFF) {
+      frameSize = data.readBits(24);
+      headerSize += 3;
+    }
+    frameSize += headerSize;
+    if (syncWord == 0xAC41) {
+      frameSize += 2;
+    }
+    int bitstreamVersion = data.readBits(2);
+    if (bitstreamVersion == 3){
+      bitstreamVersion += readVariableBits(data, 2);
+    }
+    int sequenceCounter = data.readBits(10);
+    if (data.readBits(1) == 1) {
+      if (data.readBits(3) > 0){
+        data.skipBits(2);
+      }
+    }
+    int sampleRate = (data.readBits(1) == 1) ? 48000 : 44100;
+    int frameRateIndex = data.readBits(4);
+    int sampleCount = 0;
+    if (sampleRate == 44100 && frameRateIndex == 13) {
+      sampleCount = SAMPLE_COUNT[frameRateIndex];
+    } else if (sampleRate == 48000 && frameRateIndex < SAMPLE_COUNT.length) {
+      sampleCount = SAMPLE_COUNT[frameRateIndex];
+      switch (sequenceCounter % 5) {
+        case 1:
+        case 3:
+          if (frameRateIndex == 3 || frameRateIndex == 8) {
+            sampleCount++;
+          }
+          break;
+        case 2:
+          if (frameRateIndex == 8 || frameRateIndex == 11) {
+            sampleCount++;
+          }
+          break;
+        case 4:
+          if (frameRateIndex == 3 || frameRateIndex == 8 || frameRateIndex == 11) {
+            sampleCount++;
+          }
+          break;
+        default:
+          break;
+      }
+    }
+    return new SyncFrameInfo(
+        MimeTypes.AUDIO_AC4, bitstreamVersion, CHANNEL_COUNT_2, sampleRate, frameSize, sampleCount);
+  }
+
+  /**
+   * Returns the size in bytes of the given AC-4 syncframe.
+   *
+   * @param data The syncframe to parse.
+   * @return The syncframe size in bytes. {@link C#LENGTH_UNSET} if the input is invalid.
+   */
+  public static int parseAc4SyncframeSize(byte[] data, int syncBytes) {
+    if (data.length < 7) {
+      return C.LENGTH_UNSET;
+    }
+    int headerSize = 2; // syncword
+    int frameSize = ((data[2] & 0xFF) << 8) | (data[3] & 0xFF);
+    headerSize += 2;
+    if (frameSize == 0xFFFF) {
+      frameSize = ((data[4] & 0xFF) << 16) | ((data[5] & 0xFF) << 8) | (data[6] & 0xFF);
+      headerSize += 3;
+    }
+    if (syncBytes == 0xAC41) {
+      headerSize += 2;
+    }
+    frameSize += headerSize;
+    return frameSize;
+  }
+
+  /**
+   * Reads the number of audio samples represented by the given AC-4 syncframe. The buffer's
+   * position is not modified.
+   *
+   * @param buffer The {@link ByteBuffer} from which to read the syncframe.
+   * @return The number of audio samples represented by the syncframe.
+   */
+  public static int parseAc4SyncframeAudioSampleCount(ByteBuffer buffer) {
+    byte[] bufferBytes = new byte[HEADER_SIZE_FOR_PARSER];
+    buffer.get(bufferBytes);
+    ParsableBitArray data = new ParsableBitArray(bufferBytes);
+    SyncFrameInfo ac4SyncframeInfo = parseAc4SyncframeInfo(data);
+    return ac4SyncframeInfo.sampleCount;
+  }
+
+  /**
+   * Create AC-4 sample header, which includes AC-4 syncword and frame size.
+   *
+   * @param sampleSize The size of AC-4 sample.
+   * @return The AC-4 sample header byte array.
+   */
+  public static ParsableByteArray getAc4SampleHeader(int sampleSize) {
+    // Add AC-4 Syncword 0xAC40 and frame size to create AC-4 syncframe
+    // ETSI TS 103 190-1 V1.3.1, Annex G
+    byte[] ac4SampleHeader  = new byte[] {(byte)0xAC, 0x40, (byte)0xFF, (byte)0xFF,
+        (byte)(sampleSize >> 16 & 0xFF), (byte)(sampleSize >> 8 & 0xFF), (byte)(sampleSize & 0xFF)};
+    return new ParsableByteArray(ac4SampleHeader);
+  }
+
+  private Ac4Util() {}
+
+}

library/core/src/main/java/com/google/android/exoplayer2/audio/DefaultAudioSink.java

@@ -1202,6 +1202,8 @@ public final class DefaultAudioSink implements AudioSink {
         return 18000 * 1000 / 8;
       case C.ENCODING_DOLBY_TRUEHD:
         return 24500 * 1000 / 8;
+      case C.ENCODING_AC4:
+        return 2688 * 1000 / 8;
       case C.ENCODING_INVALID:
       case C.ENCODING_PCM_16BIT:
       case C.ENCODING_PCM_24BIT:
@@ -1229,6 +1231,8 @@ public final class DefaultAudioSink implements AudioSink {
           ? 0
           : (Ac3Util.parseTrueHdSyncframeAudioSampleCount(buffer, syncframeOffset)
               * Ac3Util.TRUEHD_RECHUNK_SAMPLE_COUNT);
+    } else if (encoding == C.ENCODING_AC4) {
+      return Ac4Util.parseAc4SyncframeAudioSampleCount(buffer);
     } else {
       throw new IllegalStateException("Unexpected audio encoding: " + encoding);
     }

library/core/src/main/java/com/google/android/exoplayer2/audio/MediaCodecAudioRenderer.java

@@ -787,6 +787,11 @@ public class MediaCodecAudioRenderer extends MediaCodecRenderer implements Media
         mediaFormat.setFloat(MediaFormat.KEY_OPERATING_RATE, codecOperatingRate);
       }
     }
+    if (MimeTypes.AUDIO_AC4.equals(format.sampleMimeType)) {
+      // Some devices handle AC-4 raw frame by default.
+      // Need to notify the codec to handle AC-4 sync frame.
+      mediaFormat.setInteger("ac4-is-sync", 1);
+    }
     return mediaFormat;
   }
 

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

@@ -23,6 +23,7 @@ import com.google.android.exoplayer2.extractor.mp4.FragmentedMp4Extractor;
 import com.google.android.exoplayer2.extractor.mp4.Mp4Extractor;
 import com.google.android.exoplayer2.extractor.ogg.OggExtractor;
 import com.google.android.exoplayer2.extractor.ts.Ac3Extractor;
+import com.google.android.exoplayer2.extractor.ts.Ac4Extractor;
 import com.google.android.exoplayer2.extractor.ts.AdtsExtractor;
 import com.google.android.exoplayer2.extractor.ts.DefaultTsPayloadReaderFactory;
 import com.google.android.exoplayer2.extractor.ts.PsExtractor;
@@ -206,7 +207,7 @@ public final class DefaultExtractorsFactory implements ExtractorsFactory {
 
   @Override
   public synchronized Extractor[] createExtractors() {
-    Extractor[] extractors = new Extractor[FLAC_EXTRACTOR_CONSTRUCTOR == null ? 12 : 13];
+    Extractor[] extractors = new Extractor[FLAC_EXTRACTOR_CONSTRUCTOR == null ? 13 : 14];
     extractors[0] = new MatroskaExtractor(matroskaFlags);
     extractors[1] = new FragmentedMp4Extractor(fragmentedMp4Flags);
     extractors[2] = new Mp4Extractor(mp4Flags);
@@ -235,9 +236,10 @@ public final class DefaultExtractorsFactory implements ExtractorsFactory {
                 | (constantBitrateSeekingEnabled
                     ? AmrExtractor.FLAG_ENABLE_CONSTANT_BITRATE_SEEKING
                     : 0));
+    extractors[12] = new Ac4Extractor();
     if (FLAC_EXTRACTOR_CONSTRUCTOR != null) {
       try {
-        extractors[12] = FLAC_EXTRACTOR_CONSTRUCTOR.newInstance();
+        extractors[13] = FLAC_EXTRACTOR_CONSTRUCTOR.newInstance();
       } catch (Exception e) {
         // Should never happen.
         throw new IllegalStateException("Unexpected error creating FLAC extractor", e);

library/core/src/main/java/com/google/android/exoplayer2/extractor/mp4/Atom.java

@@ -67,6 +67,8 @@ import java.util.List;
   public static final int TYPE_dac3 = Util.getIntegerCodeForString("dac3");
   public static final int TYPE_ec_3 = Util.getIntegerCodeForString("ec-3");
   public static final int TYPE_dec3 = Util.getIntegerCodeForString("dec3");
+  public static final int TYPE_ac_4 = Util.getIntegerCodeForString("ac-4");
+  public static final int TYPE_dac4 = Util.getIntegerCodeForString("dac4");
   public static final int TYPE_dtsc = Util.getIntegerCodeForString("dtsc");
   public static final int TYPE_dtsh = Util.getIntegerCodeForString("dtsh");
   public static final int TYPE_dtsl = Util.getIntegerCodeForString("dtsl");

library/core/src/main/java/com/google/android/exoplayer2/extractor/mp4/AtomParsers.java

@@ -22,6 +22,7 @@ import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.ParserException;
 import com.google.android.exoplayer2.audio.Ac3Util;
+import com.google.android.exoplayer2.audio.Ac4Util;
 import com.google.android.exoplayer2.drm.DrmInitData;
 import com.google.android.exoplayer2.extractor.GaplessInfoHolder;
 import com.google.android.exoplayer2.metadata.Metadata;
@@ -684,6 +685,7 @@ import java.util.List;
           || childAtomType == Atom.TYPE_enca
           || childAtomType == Atom.TYPE_ac_3
           || childAtomType == Atom.TYPE_ec_3
+          || childAtomType == Atom.TYPE_ac_4
           || childAtomType == Atom.TYPE_dtsc
           || childAtomType == Atom.TYPE_dtse
           || childAtomType == Atom.TYPE_dtsh
@@ -974,6 +976,8 @@ import java.util.List;
       mimeType = MimeTypes.AUDIO_AC3;
     } else if (atomType == Atom.TYPE_ec_3) {
       mimeType = MimeTypes.AUDIO_E_AC3;
+    } else if (atomType == Atom.TYPE_ac_4) {
+      mimeType = MimeTypes.AUDIO_AC4;
     } else if (atomType == Atom.TYPE_dtsc) {
       mimeType = MimeTypes.AUDIO_DTS;
     } else if (atomType == Atom.TYPE_dtsh || atomType == Atom.TYPE_dtsl) {
@@ -1031,6 +1035,10 @@ import java.util.List;
         parent.setPosition(Atom.HEADER_SIZE + childPosition);
         out.format = Ac3Util.parseEAc3AnnexFFormat(parent, Integer.toString(trackId), language,
             drmInitData);
+      } else if (childAtomType == Atom.TYPE_dac4) {
+        parent.setPosition(Atom.HEADER_SIZE + childPosition);
+        out.format = Ac4Util.parseAc4AnnexEFormat(parent, Integer.toString(trackId), language,
+            drmInitData);
       } else if (childAtomType == Atom.TYPE_ddts) {
         out.format = Format.createAudioSampleFormat(Integer.toString(trackId), mimeType, null,
             Format.NO_VALUE, Format.NO_VALUE, channelCount, sampleRate, null, drmInitData, 0,

library/core/src/main/java/com/google/android/exoplayer2/extractor/mp4/FragmentedMp4Extractor.java

@@ -22,6 +22,7 @@ import android.util.SparseArray;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.ParserException;
+import com.google.android.exoplayer2.audio.Ac4Util;
 import com.google.android.exoplayer2.drm.DrmInitData;
 import com.google.android.exoplayer2.drm.DrmInitData.SchemeData;
 import com.google.android.exoplayer2.extractor.ChunkIndex;
@@ -1276,10 +1277,17 @@ public class FragmentedMp4Extractor implements Extractor {
         }
       }
     } else {
+      int sampleHeaderSize = 0;
+      if (MimeTypes.AUDIO_AC4.equals(track.format.sampleMimeType)) {
+        ParsableByteArray ac4SampleHeaderData = Ac4Util.getAc4SampleHeader(sampleSize);
+        output.sampleData(ac4SampleHeaderData, ac4SampleHeaderData.capacity());
+        sampleHeaderSize = ac4SampleHeaderData.capacity();
+      }
       while (sampleBytesWritten < sampleSize) {
         int writtenBytes = output.sampleData(input, sampleSize - sampleBytesWritten, false);
         sampleBytesWritten += writtenBytes;
       }
+      sampleSize += sampleHeaderSize;
     }
 
     @C.BufferFlags int sampleFlags = fragment.sampleIsSyncFrameTable[sampleIndex]

library/core/src/main/java/com/google/android/exoplayer2/extractor/mp4/Mp4Extractor.java

@@ -19,6 +19,7 @@ import android.support.annotation.IntDef;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.ParserException;
+import com.google.android.exoplayer2.audio.Ac4Util;
 import com.google.android.exoplayer2.extractor.Extractor;
 import com.google.android.exoplayer2.extractor.ExtractorInput;
 import com.google.android.exoplayer2.extractor.ExtractorOutput;
@@ -31,6 +32,7 @@ import com.google.android.exoplayer2.extractor.TrackOutput;
 import com.google.android.exoplayer2.extractor.mp4.Atom.ContainerAtom;
 import com.google.android.exoplayer2.metadata.Metadata;
 import com.google.android.exoplayer2.util.Assertions;
+import com.google.android.exoplayer2.util.MimeTypes;
 import com.google.android.exoplayer2.util.NalUnitUtil;
 import com.google.android.exoplayer2.util.ParsableByteArray;
 import com.google.android.exoplayer2.util.Util;
@@ -536,11 +538,18 @@ public final class Mp4Extractor implements Extractor, SeekMap {
         }
       }
     } else {
+      int sampleHeaderSize = 0;
+      if (MimeTypes.AUDIO_AC4.equals(track.track.format.sampleMimeType)) {
+        ParsableByteArray ac4SampleHeaderData = Ac4Util.getAc4SampleHeader(sampleSize);
+        trackOutput.sampleData(ac4SampleHeaderData, ac4SampleHeaderData.capacity());
+        sampleHeaderSize = ac4SampleHeaderData.capacity();
+      }
       while (sampleBytesWritten < sampleSize) {
         int writtenBytes = trackOutput.sampleData(input, sampleSize - sampleBytesWritten, false);
         sampleBytesWritten += writtenBytes;
         sampleCurrentNalBytesRemaining -= writtenBytes;
       }
+      sampleSize += sampleHeaderSize;
     }
     trackOutput.sampleMetadata(track.sampleTable.timestampsUs[sampleIndex],
         track.sampleTable.flags[sampleIndex], sampleSize, 0, null);

library/core/src/main/java/com/google/android/exoplayer2/extractor/ts/Ac4Extractor.java

@@ -0,0 +1,162 @@
+/*
+ * Copyright (C) 2018 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 static com.google.android.exoplayer2.extractor.ts.TsPayloadReader.FLAG_DATA_ALIGNMENT_INDICATOR;
+
+import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.audio.Ac4Util;
+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.extractor.ts.TsPayloadReader.TrackIdGenerator;
+import com.google.android.exoplayer2.util.ParsableByteArray;
+import com.google.android.exoplayer2.util.Util;
+
+import java.io.IOException;
+
+/**
+ * Extracts data from AC-4 bitstreams.
+ */
+public final class Ac4Extractor implements Extractor {
+
+  /**
+   * Factory for {@link Ac4Extractor} instances.
+   */
+  public static final ExtractorsFactory FACTORY = () -> new Extractor[] {new Ac4Extractor()};
+
+  /**
+   * 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 AC40_SYNC_WORD = 0xAC40;
+  private static final int AC41_SYNC_WORD = 0xAC41;
+  /**
+   * Typical AC-4 frame size (in bytes)
+   * The value 16 kB is determined by the maximum frame size used in broadcast applications.
+   */
+  private static final int FRAMELEN_TYPICAL = 16384;  /* in bytes (16 kB) */
+  private static final int ID3_TAG = Util.getIntegerCodeForString("ID3");
+
+  private final long firstSampleTimestampUs;
+  private final Ac4Reader reader;
+  private final ParsableByteArray sampleData;
+
+  private boolean startedPacket;
+
+  public Ac4Extractor() {
+    this(0);
+  }
+
+  public Ac4Extractor(long firstSampleTimestampUs) {
+    this.firstSampleTimestampUs = firstSampleTimestampUs;
+    reader = new Ac4Reader();
+    sampleData = new ParsableByteArray(FRAMELEN_TYPICAL);
+  }
+
+  // Extractor implementation.
+
+  @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, 7);
+      scratch.setPosition(0);
+      int syncBytes = scratch.readUnsignedShort();
+      if (syncBytes != AC40_SYNC_WORD && syncBytes != AC41_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 = Ac4Util.parseAc4SyncframeSize(scratch.data, syncBytes);
+        if (frameSize == C.LENGTH_UNSET) {
+          return false;
+        }
+        input.advancePeekPosition(frameSize - 7);
+      }
+    }
+  }
+
+  @Override
+  public void init(ExtractorOutput output) {
+    reader.createTracks(output, new TrackIdGenerator(0, 1));
+    output.endTracks();
+    output.seekMap(new SeekMap.Unseekable(C.TIME_UNSET));
+  }
+
+  @Override
+  public void seek(long position, long timeUs) {
+    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, FRAMELEN_TYPICAL);
+    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, FLAG_DATA_ALIGNMENT_INDICATOR);
+      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/core/src/main/java/com/google/android/exoplayer2/extractor/ts/Ac4Reader.java

@@ -0,0 +1,215 @@
+/*
+ * Copyright (C) 2018 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.support.annotation.IntDef;
+import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.Format;
+import com.google.android.exoplayer2.audio.Ac4Util;
+import com.google.android.exoplayer2.audio.Ac4Util.SyncFrameInfo;
+import com.google.android.exoplayer2.extractor.ExtractorOutput;
+import com.google.android.exoplayer2.extractor.TrackOutput;
+import com.google.android.exoplayer2.extractor.ts.TsPayloadReader.TrackIdGenerator;
+import com.google.android.exoplayer2.util.ParsableBitArray;
+import com.google.android.exoplayer2.util.ParsableByteArray;
+import java.lang.annotation.Documented;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+/**
+ * Parses a continuous AC-4 byte stream and extracts individual samples.
+ */
+public final class Ac4Reader implements ElementaryStreamReader {
+
+  @Documented
+  @Retention(RetentionPolicy.SOURCE)
+  @IntDef({STATE_FINDING_SYNC, STATE_READING_HEADER, STATE_READING_SAMPLE})
+  private @interface State {}
+
+  private static final int STATE_FINDING_SYNC = 0;
+  private static final int STATE_READING_HEADER = 1;
+  private static final int STATE_READING_SAMPLE = 2;
+
+  private final ParsableBitArray headerScratchBits;
+  private final ParsableByteArray headerScratchBytes;
+  private final String language;
+
+  private String trackFormatId;
+  private TrackOutput output;
+
+  @State private int state;
+  private int bytesRead;
+
+  // Used to find the header.
+  private boolean lastByteWasAC;
+  private boolean hasCRC;
+
+  // Used when parsing the header.
+  private long sampleDurationUs;
+  private Format format;
+  private int sampleSize;
+
+  // Used when reading the samples.
+  private long timeUs;
+
+  /**
+   * Constructs a new reader for AC-4 elementary streams.
+   */
+  public Ac4Reader() {
+    this(null);
+  }
+
+  /**
+   * Constructs a new reader for AC-4 elementary streams.
+   *
+   * @param language Track language.
+   */
+  public Ac4Reader(String language) {
+    headerScratchBits = new ParsableBitArray(new byte[Ac4Util.HEADER_SIZE_FOR_PARSER]);
+    headerScratchBytes = new ParsableByteArray(headerScratchBits.data);
+    state = STATE_FINDING_SYNC;
+    bytesRead = 0;
+    lastByteWasAC = false;
+    hasCRC = false;
+    this.language = language;
+  }
+
+  @Override
+  public void seek() {
+    state = STATE_FINDING_SYNC;
+    bytesRead = 0;
+    lastByteWasAC = false;
+    hasCRC = false;
+  }
+
+  @Override
+  public void createTracks(ExtractorOutput extractorOutput, TrackIdGenerator generator) {
+    generator.generateNewId();
+    trackFormatId = generator.getFormatId();
+    output = extractorOutput.track(generator.getTrackId(), C.TRACK_TYPE_AUDIO);
+  }
+
+  @Override
+  public void packetStarted(long pesTimeUs, @TsPayloadReader.Flags int flags) {
+    timeUs = pesTimeUs;
+  }
+
+  @Override
+  public void consume(ParsableByteArray data) {
+    while (data.bytesLeft() > 0) {
+      switch (state) {
+        case STATE_FINDING_SYNC:
+          if (skipToNextSync(data)) {
+            state = STATE_READING_HEADER;
+            headerScratchBytes.data[0] = (byte)0xAC;
+            headerScratchBytes.data[1] = 0x40;
+            if (hasCRC)
+              headerScratchBytes.data[1] = 0x41;
+            bytesRead = 2;
+          }
+          break;
+        case STATE_READING_HEADER:
+          if (continueRead(data, headerScratchBytes.data, Ac4Util.HEADER_SIZE_FOR_PARSER)) {
+            parseHeader();
+            headerScratchBytes.setPosition(0);
+            output.sampleData(headerScratchBytes, Ac4Util.HEADER_SIZE_FOR_PARSER);
+            state = STATE_READING_SAMPLE;
+          }
+          break;
+        case STATE_READING_SAMPLE:
+          int bytesToRead = Math.min(data.bytesLeft(), sampleSize - bytesRead);
+          output.sampleData(data, bytesToRead);
+          bytesRead += bytesToRead;
+          if (bytesRead == sampleSize) {
+            output.sampleMetadata(timeUs, C.BUFFER_FLAG_KEY_FRAME, sampleSize, 0, null);
+            timeUs += sampleDurationUs;
+            state = STATE_FINDING_SYNC;
+          }
+          break;
+        default:
+          break;
+      }
+    }
+  }
+
+  @Override
+  public void packetFinished() {
+    // Do nothing.
+  }
+
+  /**
+   * Continues a read from the provided {@code source} into a given {@code target}. It's assumed
+   * that the data should be written into {@code target} starting from an offset of zero.
+   *
+   * @param source The source from which to read.
+   * @param target The target into which data is to be read.
+   * @param targetLength The target length of the read.
+   * @return Whether the target length was reached.
+   */
+  private boolean continueRead(ParsableByteArray source, byte[] target, int targetLength) {
+    int bytesToRead = Math.min(source.bytesLeft(), targetLength - bytesRead);
+    source.readBytes(target, bytesRead, bytesToRead);
+    bytesRead += bytesToRead;
+    return bytesRead == targetLength;
+  }
+
+  /**
+   * Locates the next syncword, advancing the position to the byte that immediately follows it. If a
+   * syncword was not located, the position is advanced to the limit.
+   *
+   * @param pesBuffer The buffer whose position should be advanced.
+   * @return Whether a syncword position was found.
+   */
+  private boolean skipToNextSync(ParsableByteArray pesBuffer) {
+    while (pesBuffer.bytesLeft() > 0) {
+      if (!lastByteWasAC) {
+        lastByteWasAC = (pesBuffer.readUnsignedByte() == 0xAC);
+        continue;
+      }
+      int secondByte = pesBuffer.readUnsignedByte();
+      if (secondByte == 0x40 || secondByte == 0x41) {
+        lastByteWasAC = false;
+        hasCRC = (secondByte == 0x41);
+        return true;
+      } else {
+        lastByteWasAC = (secondByte == 0xAC);
+      }
+    }
+    return false;
+  }
+
+  /**
+   * Parses the sample header.
+   */
+  @SuppressWarnings("ReferenceEquality")
+  private void parseHeader() {
+    headerScratchBits.setPosition(0);
+    SyncFrameInfo frameInfo = Ac4Util.parseAc4SyncframeInfo(headerScratchBits);
+    if (format == null || frameInfo.channelCount != format.channelCount
+        || frameInfo.sampleRate != format.sampleRate
+        || frameInfo.mimeType != format.sampleMimeType) {
+      format = Format.createAudioSampleFormat(trackFormatId, frameInfo.mimeType, null,
+          Format.NO_VALUE, Format.NO_VALUE, frameInfo.channelCount, frameInfo.sampleRate, null,
+          null, 0, language);
+      output.format(format);
+    }
+    sampleSize = frameInfo.frameSize;
+    // In this class a sample is an AC-4 sync frame, but the MediaFormat sample rate specifies the
+    // number of PCM audio samples per second.
+    sampleDurationUs = C.MICROS_PER_SECOND * frameInfo.sampleCount / format.sampleRate;
+  }
+
+}

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

@@ -142,6 +142,8 @@ public final class DefaultTsPayloadReaderFactory implements TsPayloadReader.Fact
       case TsExtractor.TS_STREAM_TYPE_AC3:
       case TsExtractor.TS_STREAM_TYPE_E_AC3:
         return new PesReader(new Ac3Reader(esInfo.language));
+      case TsExtractor.TS_STREAM_TYPE_AC4:
+        return new PesReader(new Ac4Reader(esInfo.language));
       case TsExtractor.TS_STREAM_TYPE_DTS:
       case TsExtractor.TS_STREAM_TYPE_HDMV_DTS:
         return new PesReader(new DtsReader(esInfo.language));

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

@@ -85,6 +85,7 @@ public final class TsExtractor implements Extractor {
   public static final int TS_STREAM_TYPE_DTS = 0x8A;
   public static final int TS_STREAM_TYPE_HDMV_DTS = 0x82;
   public static final int TS_STREAM_TYPE_E_AC3 = 0x87;
+  public static final int TS_STREAM_TYPE_AC4 = 0xAC;  /* DVB/ATSC AC-4 Descriptor */
   public static final int TS_STREAM_TYPE_H262 = 0x02;
   public static final int TS_STREAM_TYPE_H264 = 0x1B;
   public static final int TS_STREAM_TYPE_H265 = 0x24;
@@ -100,6 +101,7 @@ public final class TsExtractor implements Extractor {
 
   private static final long AC3_FORMAT_IDENTIFIER = Util.getIntegerCodeForString("AC-3");
   private static final long E_AC3_FORMAT_IDENTIFIER = Util.getIntegerCodeForString("EAC3");
+  private static final long AC4_FORMAT_IDENTIFIER = Util.getIntegerCodeForString("AC-4");
   private static final long HEVC_FORMAT_IDENTIFIER = Util.getIntegerCodeForString("HEVC");
 
   private static final int BUFFER_SIZE = TS_PACKET_SIZE * 50;
@@ -484,8 +486,11 @@ public final class TsExtractor implements Extractor {
     private static final int TS_PMT_DESC_AC3 = 0x6A;
     private static final int TS_PMT_DESC_EAC3 = 0x7A;
     private static final int TS_PMT_DESC_DTS = 0x7B;
+    private static final int TS_PMT_DESC_DVB_EXT = 0x7F;
     private static final int TS_PMT_DESC_DVBSUBS = 0x59;
 
+    private static final int TS_PMT_DESC_DVB_EXT_AC4 = 0x15;
+
     private final ParsableBitArray pmtScratch;
     private final SparseArray<TsPayloadReader> trackIdToReaderScratch;
     private final SparseIntArray trackIdToPidScratch;
@@ -638,6 +643,8 @@ public final class TsExtractor implements Extractor {
             streamType = TS_STREAM_TYPE_AC3;
           } else if (formatIdentifier == E_AC3_FORMAT_IDENTIFIER) {
             streamType = TS_STREAM_TYPE_E_AC3;
+          } else if (formatIdentifier == AC4_FORMAT_IDENTIFIER) {
+            streamType = TS_STREAM_TYPE_AC4;
           } else if (formatIdentifier == HEVC_FORMAT_IDENTIFIER) {
             streamType = TS_STREAM_TYPE_H265;
           }
@@ -645,6 +652,13 @@ public final class TsExtractor implements Extractor {
           streamType = TS_STREAM_TYPE_AC3;
         } else if (descriptorTag == TS_PMT_DESC_EAC3) { // enhanced_AC-3_descriptor
           streamType = TS_STREAM_TYPE_E_AC3;
+        } else if (descriptorTag == TS_PMT_DESC_DVB_EXT) {
+          // extension descriptor in DVB (ETSI EN 300 468)
+          int descriptorTagExt = data.readUnsignedByte();
+          if (descriptorTagExt == TS_PMT_DESC_DVB_EXT_AC4) {
+            // AC-4_descriptor in DVB (ETSI EN 300 468)
+            streamType = TS_STREAM_TYPE_AC4;
+          }
         } else if (descriptorTag == TS_PMT_DESC_DTS) { // DTS_descriptor
           streamType = TS_STREAM_TYPE_DTS;
         } else if (descriptorTag == TS_PMT_DESC_ISO639_LANG) {

library/core/src/main/java/com/google/android/exoplayer2/util/MimeTypes.java

@@ -55,6 +55,7 @@ public final class MimeTypes {
   public static final String AUDIO_AC3 = BASE_TYPE_AUDIO + "/ac3";
   public static final String AUDIO_E_AC3 = BASE_TYPE_AUDIO + "/eac3";
   public static final String AUDIO_E_AC3_JOC = BASE_TYPE_AUDIO + "/eac3-joc";
+  public static final String AUDIO_AC4 = BASE_TYPE_AUDIO + "/ac4";
   public static final String AUDIO_TRUEHD = BASE_TYPE_AUDIO + "/true-hd";
   public static final String AUDIO_DTS = BASE_TYPE_AUDIO + "/vnd.dts";
   public static final String AUDIO_DTS_HD = BASE_TYPE_AUDIO + "/vnd.dts.hd";
@@ -237,6 +238,8 @@ public final class MimeTypes {
       return MimeTypes.AUDIO_E_AC3;
     } else if (codec.startsWith("ec+3")) {
       return MimeTypes.AUDIO_E_AC3_JOC;
+    } else if (codec.startsWith("ac-4") || codec.startsWith("dac4")) {
+      return MimeTypes.AUDIO_AC4;
     } else if (codec.startsWith("dtsc") || codec.startsWith("dtse")) {
       return MimeTypes.AUDIO_DTS;
     } else if (codec.startsWith("dtsh") || codec.startsWith("dtsl")) {
@@ -301,6 +304,8 @@ public final class MimeTypes {
         return MimeTypes.AUDIO_DTS_HD;
       case 0xAD:
         return MimeTypes.AUDIO_OPUS;
+      case 0xAE:
+        return MimeTypes.AUDIO_AC4;
       default:
         return null;
     }
@@ -354,6 +359,8 @@ public final class MimeTypes {
       case MimeTypes.AUDIO_E_AC3:
       case MimeTypes.AUDIO_E_AC3_JOC:
         return C.ENCODING_E_AC3;
+      case MimeTypes.AUDIO_AC4:
+        return C.ENCODING_AC4;
       case MimeTypes.AUDIO_DTS:
         return C.ENCODING_DTS;
       case MimeTypes.AUDIO_DTS_HD:

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/DefaultHlsExtractorFactory.java

@@ -25,6 +25,7 @@ import com.google.android.exoplayer2.extractor.ExtractorInput;
 import com.google.android.exoplayer2.extractor.mp3.Mp3Extractor;
 import com.google.android.exoplayer2.extractor.mp4.FragmentedMp4Extractor;
 import com.google.android.exoplayer2.extractor.ts.Ac3Extractor;
+import com.google.android.exoplayer2.extractor.ts.Ac4Extractor;
 import com.google.android.exoplayer2.extractor.ts.AdtsExtractor;
 import com.google.android.exoplayer2.extractor.ts.DefaultTsPayloadReaderFactory;
 import com.google.android.exoplayer2.extractor.ts.TsExtractor;
@@ -43,6 +44,7 @@ public final class DefaultHlsExtractorFactory implements HlsExtractorFactory {
 
   public static final String AAC_FILE_EXTENSION = ".aac";
   public static final String AC3_FILE_EXTENSION = ".ac3";
+  public static final String AC4_FILE_EXTENSION = ".ac4";
   public static final String EC3_FILE_EXTENSION = ".ec3";
   public static final String MP3_FILE_EXTENSION = ".mp3";
   public static final String MP4_FILE_EXTENSION = ".mp4";
@@ -94,6 +96,8 @@ public final class DefaultHlsExtractorFactory implements HlsExtractorFactory {
         return buildResult(new AdtsExtractor());
       } else if (previousExtractor instanceof Ac3Extractor) {
         return buildResult(new Ac3Extractor());
+      } else if (previousExtractor instanceof Ac4Extractor) {
+        return buildResult(new Ac4Extractor());
       } else if (previousExtractor instanceof Mp3Extractor) {
         return buildResult(new Mp3Extractor());
       } else {
@@ -135,6 +139,13 @@ public final class DefaultHlsExtractorFactory implements HlsExtractorFactory {
       }
     }
 
+    if (!(extractorByFileExtension instanceof Ac4Extractor)) {
+      Ac4Extractor ac4Extractor = new Ac4Extractor();
+      if (sniffQuietly(ac4Extractor, extractorInput)) {
+        return buildResult(ac4Extractor);
+      }
+    }
+
     if (!(extractorByFileExtension instanceof Mp3Extractor)) {
       Mp3Extractor mp3Extractor =
           new Mp3Extractor(/* flags= */ 0, /* forcedFirstSampleTimestampUs= */ 0);
@@ -188,6 +199,8 @@ public final class DefaultHlsExtractorFactory implements HlsExtractorFactory {
     } else if (lastPathSegment.endsWith(AC3_FILE_EXTENSION)
         || lastPathSegment.endsWith(EC3_FILE_EXTENSION)) {
       return new Ac3Extractor();
+    } else if (lastPathSegment.endsWith(AC4_FILE_EXTENSION)) {
+      return new Ac4Extractor();
     } else if (lastPathSegment.endsWith(MP3_FILE_EXTENSION)) {
       return new Mp3Extractor(/* flags= */ 0, /* forcedFirstSampleTimestampUs= */ 0);
     } else if (lastPathSegment.endsWith(MP4_FILE_EXTENSION)
@@ -254,6 +267,7 @@ public final class DefaultHlsExtractorFactory implements HlsExtractorFactory {
         extractor,
         extractor instanceof AdtsExtractor
             || extractor instanceof Ac3Extractor
+            || extractor instanceof Ac4Extractor
             || extractor instanceof Mp3Extractor);
   }