Search for synch' when sniffing ADTS and check four frames.

Issue: #791

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

@@ -20,6 +20,7 @@ import com.google.android.exoplayer.extractor.ExtractorInput;
 import com.google.android.exoplayer.extractor.ExtractorOutput;
 import com.google.android.exoplayer.extractor.PositionHolder;
 import com.google.android.exoplayer.extractor.SeekMap;
+import com.google.android.exoplayer.util.ParsableBitArray;
 import com.google.android.exoplayer.util.ParsableByteArray;
 import com.google.android.exoplayer.util.Util;
 
@@ -32,6 +33,12 @@ import java.io.IOException;
 public final class AdtsExtractor implements Extractor {
 
   private static final int MAX_PACKET_SIZE = 200;
+  private static final int ID3_TAG = Util.getIntegerCodeForString("ID3");
+  /**
+   * The maximum number of bytes to search when sniffing, excluding the header, before giving up.
+   * Frame sizes are represented by 13-bit fields, so expect a valid frame in the first 8192 bytes.
+   */
+  private static final int MAX_SNIFF_BYTES = 8 * 1024;
 
   private final long firstSampleTimestampUs;
   private final ParsableByteArray packetBuffer;
@@ -52,20 +59,53 @@ public final class AdtsExtractor implements Extractor {
 
   @Override
   public boolean sniff(ExtractorInput input) throws IOException, InterruptedException {
+    // Skip any ID3 headers.
     ParsableByteArray scratch = new ParsableByteArray(10);
-    input.peekFully(scratch.data, 0, 10);
-    int value = scratch.readUnsignedInt24();
-    if (value != Util.getIntegerCodeForString("ID3")) {
-      value = value >> 8;
-    } else {
+    ParsableBitArray scratchBits = new ParsableBitArray(scratch.data);
+    int startPosition = 0;
+    while (true) {
+      input.peekFully(scratch.data, 0, 10);
+      scratch.setPosition(0);
+      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);
+      startPosition += 10 + length;
       input.advancePeekPosition(length);
+    }
+    input.resetPeekPosition();
+    input.advancePeekPosition(startPosition);
+
+    // Try to find four or more consecutive AAC audio frames, exceeding the MPEG TS packet size.
+    int headerPosition = startPosition;
+    int validFramesSize = 0;
+    int validFramesCount = 0;
+    while (true) {
       input.peekFully(scratch.data, 0, 2);
       scratch.setPosition(0);
-      value = scratch.readUnsignedShort();
+      int syncBytes = scratch.readUnsignedShort();
+      if ((syncBytes & 0xFFF6) != 0xFFF0) {
+        validFramesCount = 0;
+        validFramesSize = 0;
+        input.resetPeekPosition();
+        if (++headerPosition - startPosition >= MAX_SNIFF_BYTES) {
+          return false;
+        }
+        input.advancePeekPosition(headerPosition);
+      } else {
+        if (++validFramesCount >= 4 && validFramesSize > 188) {
+          return true;
+        }
+
+        // Skip the frame.
+        input.peekFully(scratch.data, 0, 4);
+        scratchBits.setPosition(14);
+        int frameSize = scratchBits.readBits(13);
+        input.advancePeekPosition(frameSize - 6);
+        validFramesSize += frameSize;
+      }
     }
-    return (value & 0xFFF6) == 0xFFF0;
   }
 
   @Override