Use streaminfo block for FLAC files.

RELEASENOTES.md

@@ -57,6 +57,10 @@
 *   Smooth Streaming extension:
 *   RTSP extension:
 *   Decoder extensions (FFmpeg, VP9, AV1, etc.):
+    *   FFmpeg extension: Fix an issue that prevented some FLAC files from
+        playing by ensuring the `STREAMINFO` block is correctly parsed and
+        passed to the decoder
+        ([#2887](https://github.com/androidx/media/issues/2887)).
 *   MIDI extension:
 *   Leanback extension:
 *   Cast extension:

libraries/decoder_ffmpeg/src/main/java/androidx/media3/decoder/ffmpeg/FfmpegAudioDecoder.java

@@ -39,6 +39,12 @@
   private static final int AUDIO_DECODER_ERROR_INVALID_DATA = -1;
   private static final int AUDIO_DECODER_ERROR_OTHER = -2;
 
+  // FLAC parsing constants
+  private static final byte[] flacStreamMarker = {'f', 'L', 'a', 'C'};
+  private static final int FLAC_METADATA_TYPE_STREAM_INFO = 0;
+  private static final int FLAC_METADATA_BLOCK_HEADER_SIZE = 4;
+  private static final int FLAC_STREAM_INFO_DATA_SIZE = 34;
+
   private final String codecName;
   @Nullable private final byte[] extraData;
   private final @C.PcmEncoding int encoding;
@@ -190,6 +196,8 @@ private static byte[] getExtraData(String mimeType, List<byte[]> initializationD
         return getAlacExtraData(initializationData);
       case MimeTypes.AUDIO_VORBIS:
         return getVorbisExtraData(initializationData);
+      case MimeTypes.AUDIO_FLAC:
+        return getFlacExtraData(initializationData);
       default:
         // Other codecs do not require extra data.
         return null;
@@ -227,6 +235,71 @@ private static byte[] getVorbisExtraData(List<byte[]> initializationData) {
     return extraData;
   }
 
+  @Nullable
+  private static byte[] getFlacExtraData(List<byte[]> initializationData) {
+    for (int i = 0; i < initializationData.size(); i++) {
+      byte[] out = extractFlacStreamInfo(initializationData.get(i));
+      if (out != null) {
+        return out;
+      }
+    }
+    return null;
+  }
+
+  @Nullable
+  private static byte[] extractFlacStreamInfo(byte[] data) {
+    int offset = 0;
+    if (arrayStartsWith(data, flacStreamMarker)) {
+      offset = flacStreamMarker.length;
+    }
+
+
+    if (data.length - offset == FLAC_STREAM_INFO_DATA_SIZE) {
+      byte[] streamInfo = new byte[FLAC_STREAM_INFO_DATA_SIZE];
+      System.arraycopy(data, offset, streamInfo, 0, FLAC_STREAM_INFO_DATA_SIZE);
+      return streamInfo;
+    }
+
+    if (data.length >= offset + FLAC_METADATA_BLOCK_HEADER_SIZE) {
+      int type = data[offset] & 0x7F;
+      int length =
+          ((data[offset + 1] & 0xFF) << 16)
+              | ((data[offset + 2] & 0xFF) << 8)
+              | (data[offset + 3] & 0xFF);
+
+      if (type == FLAC_METADATA_TYPE_STREAM_INFO
+          && length == FLAC_STREAM_INFO_DATA_SIZE
+          && data.length
+          >= offset
+          + FLAC_METADATA_BLOCK_HEADER_SIZE
+          + FLAC_STREAM_INFO_DATA_SIZE) {
+        byte[] streamInfo = new byte[FLAC_STREAM_INFO_DATA_SIZE];
+        System.arraycopy(
+            data,
+            offset + FLAC_METADATA_BLOCK_HEADER_SIZE,
+            streamInfo,
+            0,
+            FLAC_STREAM_INFO_DATA_SIZE);
+        return streamInfo;
+      }
+    }
+
+    return null;
+  }
+
+  private static boolean arrayStartsWith(byte[] data, byte[] prefix) {
+    if (data.length < prefix.length) {
+      return false;
+    }
+    for (int i = 0; i < prefix.length; i++) {
+      if (data[i] != prefix[i]) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+
   private native long ffmpegInitialize(
       String codecName,
       @Nullable byte[] extraData,