Standardize ALAC initialization data

Android considers ALAC initialization data to consider of the magic cookie only, where-as FFmpeg requires a full atom. Standardize around the Android definition, since it makes more sense (the magic cookie being contained within an atom is container specific, where-as the decoder shouldn't care what container the media stream is carried in) Issue: #5938 PiperOrigin-RevId: 261124155
google · Aug 1, 2019 · 23ace19 · 23ace19
1 parent 520275e
commit 23ace19
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Showing 2 changed files with 35 additions and 18 deletions.
diff --git a/extensions/ffmpeg/src/main/java/com/google/android/exoplayer2/ext/ffmpeg/FfmpegDecoder.java b/extensions/ffmpeg/src/main/java/com/google/android/exoplayer2/ext/ffmpeg/FfmpegDecoder.java
@@ -172,28 +172,49 @@ public int getSampleRate() {
   private static @Nullable byte[] getExtraData(String mimeType, List<byte[]> initializationData) {
     switch (mimeType) {
       case MimeTypes.AUDIO_AAC:
-      case MimeTypes.AUDIO_ALAC:
       case MimeTypes.AUDIO_OPUS:
         return initializationData.get(0);
+      case MimeTypes.AUDIO_ALAC:
+        return getAlacExtraData(initializationData);
       case MimeTypes.AUDIO_VORBIS:
-        byte[] header0 = initializationData.get(0);
-        byte[] header1 = initializationData.get(1);
-        byte[] extraData = new byte[header0.length + header1.length + 6];
-        extraData[0] = (byte) (header0.length >> 8);
-        extraData[1] = (byte) (header0.length & 0xFF);
-        System.arraycopy(header0, 0, extraData, 2, header0.length);
-        extraData[header0.length + 2] = 0;
-        extraData[header0.length + 3] = 0;
-        extraData[header0.length + 4] =  (byte) (header1.length >> 8);
-        extraData[header0.length + 5] = (byte) (header1.length & 0xFF);
-        System.arraycopy(header1, 0, extraData, header0.length + 6, header1.length);
-        return extraData;
+        return getVorbisExtraData(initializationData);
       default:
         // Other codecs do not require extra data.
         return null;
     }
   }
 
+  private static byte[] getAlacExtraData(List<byte[]> initializationData) {
+    // FFmpeg's ALAC decoder expects an ALAC atom, which contains the ALAC "magic cookie", as extra
+    // data. initializationData[0] contains only the magic cookie, and so we need to package it into
+    // an ALAC atom. See:
+    // https://ffmpeg.org/doxygen/0.6/alac_8c.html
+    // https://github.com/macosforge/alac/blob/master/ALACMagicCookieDescription.txt
+    byte[] magicCookie = initializationData.get(0);
+    int alacAtomLength = 12 + magicCookie.length;
+    ByteBuffer alacAtom = ByteBuffer.allocate(alacAtomLength);
+    alacAtom.putInt(alacAtomLength);
+    alacAtom.putInt(0x616c6163); // type=alac
+    alacAtom.putInt(0); // version=0, flags=0
+    alacAtom.put(magicCookie, /* offset= */ 0, magicCookie.length);
+    return alacAtom.array();
+  }
+
+  private static byte[] getVorbisExtraData(List<byte[]> initializationData) {
+    byte[] header0 = initializationData.get(0);
+    byte[] header1 = initializationData.get(1);
+    byte[] extraData = new byte[header0.length + header1.length + 6];
+    extraData[0] = (byte) (header0.length >> 8);
+    extraData[1] = (byte) (header0.length & 0xFF);
+    System.arraycopy(header0, 0, extraData, 2, header0.length);
+    extraData[header0.length + 2] = 0;
+    extraData[header0.length + 3] = 0;
+    extraData[header0.length + 4] = (byte) (header1.length >> 8);
+    extraData[header0.length + 5] = (byte) (header1.length & 0xFF);
+    System.arraycopy(header1, 0, extraData, header0.length + 6, header1.length);
+    return extraData;
+  }
+
   private native long ffmpegInitialize(
       String codecName,
       @Nullable byte[] extraData,

diff --git a/library/core/src/main/java/com/google/android/exoplayer2/extractor/mp4/AtomParsers.java b/library/core/src/main/java/com/google/android/exoplayer2/extractor/mp4/AtomParsers.java
@@ -1140,10 +1140,6 @@ private static void parseAudioSampleEntry(ParsableByteArray parent, int atomType
         out.format = Format.createAudioSampleFormat(Integer.toString(trackId), mimeType, null,
             Format.NO_VALUE, Format.NO_VALUE, channelCount, sampleRate, null, drmInitData, 0,
             language);
-      } else if (childAtomType == Atom.TYPE_alac) {
-        initializationData = new byte[childAtomSize];
-        parent.setPosition(childPosition);
-        parent.readBytes(initializationData, /* offset= */ 0, childAtomSize);
       } else if (childAtomType == Atom.TYPE_dOps) {
         // Build an Opus Identification Header (defined in RFC-7845) by concatenating the Opus Magic
         // Signature and the body of the dOps atom.
@@ -1152,7 +1148,7 @@ private static void parseAudioSampleEntry(ParsableByteArray parent, int atomType
         System.arraycopy(opusMagic, 0, initializationData, 0, opusMagic.length);
         parent.setPosition(childPosition + Atom.HEADER_SIZE);
         parent.readBytes(initializationData, opusMagic.length, childAtomBodySize);
-      } else if (childAtomSize == Atom.TYPE_dfLa) {
+      } else if (childAtomSize == Atom.TYPE_dfLa || childAtomType == Atom.TYPE_alac) {
         int childAtomBodySize = childAtomSize - Atom.FULL_HEADER_SIZE;
         initializationData = new byte[childAtomBodySize];
         parent.setPosition(childPosition + Atom.FULL_HEADER_SIZE);