support zlib compressed PGS subtitles

library/core/src/main/java/com/google/android/exoplayer2/text/pgs/PgsDecoder.java

@@ -25,6 +25,10 @@ import com.google.android.exoplayer2.util.Util;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
+import java.io.ByteArrayOutputStream;
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.util.zip.InflaterInputStream;
 
 /** A {@link SimpleSubtitleDecoder} for PGS subtitles. */
 public final class PgsDecoder extends SimpleSubtitleDecoder {
@@ -34,18 +38,29 @@ public final class PgsDecoder extends SimpleSubtitleDecoder {
   private static final int SECTION_TYPE_IDENTIFIER = 0x16;
   private static final int SECTION_TYPE_END = 0x80;
 
+  private static final int INFLATE_HEADER = 0x78;
+  private static final int INFLATE_BUFFER_SIZE = 5;
+
   private final ParsableByteArray buffer;
   private final CueBuilder cueBuilder;
+  private final ByteArrayOutputStream inflateBuffer;
+  private final byte[] inflateReadBuffer;
 
   public PgsDecoder() {
     super("PgsDecoder");
     buffer = new ParsableByteArray();
     cueBuilder = new CueBuilder();
+    inflateBuffer = new ByteArrayOutputStream();
+    inflateReadBuffer = new byte[INFLATE_BUFFER_SIZE];
   }
 
   @Override
   protected Subtitle decode(byte[] data, int size, boolean reset) throws SubtitleDecoderException {
-    buffer.reset(data, size);
+    byte[] inflated = tryInflateBuffer(data, size);
+    if (inflated == null)
+      buffer.reset(data, size);
+    else
+      buffer.reset(inflated, inflated.length);
     cueBuilder.reset();
     ArrayList<Cue> cues = new ArrayList<>();
     while (buffer.bytesLeft() >= 3) {
@@ -57,6 +72,25 @@ public final class PgsDecoder extends SimpleSubtitleDecoder {
     return new PgsSubtitle(Collections.unmodifiableList(cues));
   }
 
+  private byte[] tryInflateBuffer(byte[] data, int size) {
+    if (size > 0 && (((int) data[0]) & 0xff) != INFLATE_HEADER) return null;
+
+    inflateBuffer.reset();
+
+    try {
+      InflaterInputStream iis = new InflaterInputStream(new ByteArrayInputStream(data, 0, size));
+      int len = -1;
+
+      while ((len = iis.read(inflateReadBuffer)) != -1) {
+        inflateBuffer.write(inflateReadBuffer, 0, len);
+      }
+      return inflateBuffer.toByteArray();
+    }
+    catch (IOException e) { }
+
+    return null;
+  }
+
   private static Cue readNextSection(ParsableByteArray buffer, CueBuilder cueBuilder) {
     int limit = buffer.limit();
     int sectionType = buffer.readUnsignedByte();