webm_extractor: Fix issue in vorbis extraction.

Vorbis decoder in android MediaCodec [1] expects the last 4 bytes of the sample to be the number of samples in the current page. This definition holds good only for Ogg and is irrelevant for WebM. So we always set this to -1 (the decoder will ignore this value if we set it to -1). The android platform media extractor [2] does the same.

library/src/main/java/com/google/android/exoplayer/extractor/webm/WebmExtractor.java

@@ -104,6 +104,7 @@ public final class WebmExtractor implements Extractor {
   private final EbmlReader reader;
   private final EbmlReader reader;
   private final VarintReader varintReader;
   private final VarintReader varintReader;
   private final ParsableByteArray sampleHeaderScratch;
   private final ParsableByteArray sampleHeaderScratch;
+  private ParsableByteArray vorbisNumPageSamples;
 
 
   private long segmentContentPosition = UNKNOWN;
   private long segmentContentPosition = UNKNOWN;
   private long segmentContentSize = UNKNOWN;
   private long segmentContentSize = UNKNOWN;
@@ -468,6 +469,23 @@ public final class WebmExtractor implements Extractor {
           blockBytesRead += trackOutput.sampleData(input, contentSize - blockBytesRead);
           blockBytesRead += trackOutput.sampleData(input, contentSize - blockBytesRead);
         }
         }
 
 
+        if (CODEC_ID_VORBIS.equals(codecId)) {
+          // Vorbis decoder in android MediaCodec [1] expects the last 4 bytes of the sample to be
+          // the number of samples in the current page. This definition holds good only for Ogg and
+          // irrelevant for WebM. So we always set this to -1 (the decoder will ignore this value if
+          // we set it to -1). The android platform media extractor [2] does the same.
+          // [1] https://android.googlesource.com/platform/frameworks/av/+/lollipop-release/media/libstagefright/codecs/vorbis/dec/SoftVorbis.cpp#314
+          // [2] https://android.googlesource.com/platform/frameworks/av/+/lollipop-release/media/libstagefright/NuMediaExtractor.cpp#474
+          if (vorbisNumPageSamples == null) {
+            vorbisNumPageSamples =
+                new ParsableByteArray(ByteBuffer.allocate(4).putInt(-1).array());
+          } else {
+            vorbisNumPageSamples.setPosition(0);
+          }
+          trackOutput.sampleData(vorbisNumPageSamples, 4);
+          sampleSize += 4;
+        }
+
         trackOutput.sampleMetadata(sampleTimeUs, sampleFlags, sampleSize, 0, null);
         trackOutput.sampleMetadata(sampleTimeUs, sampleFlags, sampleSize, 0, null);
         sampleState = SAMPLE_STATE_START;
         sampleState = SAMPLE_STATE_START;
         sampleRead = true;
         sampleRead = true;