Use separate mimeType for CEA-608 embedded in MP4

When CEA-608 is embedded in MP4 each packet consists of
cc_data_1 and cc_data_2 only. The marker_bits, cc_valid
and cc_type are implicit. As a result playback of CEA-608
embedded in MP4 broke when we started passing the extra
byte for the TS case (and adjusted the decoder to assume
the byte was present).

This change introduces a special mimeType for the case
where the byte is implicit (!). An alternative option
was to insert the extra byte every 2 bytes in the MP4
extractor, but this is really quite fiddly to get right.

Also made the loops in the 608/708 decoders robust against
input of the wrong length.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=140609304

library/src/main/java/com/google/android/exoplayer2/extractor/mp4/AtomParsers.java

@@ -621,8 +621,9 @@ import java.util.List;
             MimeTypes.APPLICATION_TTML, null, Format.NO_VALUE, 0, language, drmInitData,
             0 /* subsample timing is absolute */);
       } else if (childAtomType == Atom.TYPE_c608) {
+        // Defined by the QuickTime File Format specification.
         out.format = Format.createTextSampleFormat(Integer.toString(trackId),
-            MimeTypes.APPLICATION_CEA608, null, Format.NO_VALUE, 0, language, drmInitData);
+            MimeTypes.APPLICATION_MP4CEA608, null, Format.NO_VALUE, 0, language, drmInitData);
         out.requiredSampleTransformation = Track.TRANSFORMATION_CEA608_CDAT;
       } else if (childAtomType == Atom.TYPE_camm) {
         out.format = Format.createSampleFormat(Integer.toString(trackId),

library/src/main/java/com/google/android/exoplayer2/text/SubtitleDecoderFactory.java

@@ -75,8 +75,8 @@ public interface SubtitleDecoderFactory {
           throw new IllegalArgumentException("Attempted to create decoder for unsupported format");
         }
         if (clazz == Cea608Decoder.class) {
-          return clazz.asSubclass(SubtitleDecoder.class)
-              .getConstructor(Integer.TYPE).newInstance(format.accessibilityChannel);
+          return clazz.asSubclass(SubtitleDecoder.class).getConstructor(String.class, Integer.TYPE)
+              .newInstance(format.sampleMimeType, format.accessibilityChannel);
         } else {
           return clazz.asSubclass(SubtitleDecoder.class).getConstructor().newInstance();
         }
@@ -102,6 +102,7 @@ public interface SubtitleDecoderFactory {
           case MimeTypes.APPLICATION_TX3G:
             return Class.forName("com.google.android.exoplayer2.text.tx3g.Tx3gDecoder");
           case MimeTypes.APPLICATION_CEA608:
+          case MimeTypes.APPLICATION_MP4CEA608:
             return Class.forName("com.google.android.exoplayer2.text.cea.Cea608Decoder");
           default:
             return null;

library/src/main/java/com/google/android/exoplayer2/text/cea/Cea608Decoder.java

@@ -21,6 +21,7 @@ import com.google.android.exoplayer2.text.Cue;
 import com.google.android.exoplayer2.text.Subtitle;
 import com.google.android.exoplayer2.text.SubtitleDecoder;
 import com.google.android.exoplayer2.text.SubtitleInputBuffer;
+import com.google.android.exoplayer2.util.MimeTypes;
 import com.google.android.exoplayer2.util.ParsableByteArray;
 
 /**
@@ -52,6 +53,10 @@ public final class Cea608Decoder extends CeaDecoder {
   // The default number of rows to display in roll-up captions mode.
   private static final int DEFAULT_CAPTIONS_ROW_COUNT = 4;
 
+  // An implied first byte for packets that are only 2 bytes long, consisting of marker bits
+  // (0b11111) + valid bit (0b1) + NTSC field 1 type bits (0b00).
+  private static final byte CC_IMPLICIT_DATA_HEADER = (byte) 0xFC;
+
   /**
    * Command initiating pop-on style captioning. Subsequent data should be loaded into a
    * non-displayed memory and held there until the {@link #CTRL_END_OF_CAPTION} command is received,
@@ -164,9 +169,8 @@ public final class Cea608Decoder extends CeaDecoder {
   };
 
   private final ParsableByteArray ccData;
-
   private final StringBuilder captionStringBuilder;
-
+  private final int packetLength;
   private final int selectedField;
 
   private int captionMode;
@@ -179,10 +183,11 @@ public final class Cea608Decoder extends CeaDecoder {
   private byte repeatableControlCc1;
   private byte repeatableControlCc2;
 
-  public Cea608Decoder(int accessibilityChannel) {
+  public Cea608Decoder(String mimeType, int accessibilityChannel) {
     ccData = new ParsableByteArray();
-
     captionStringBuilder = new StringBuilder();
+
+    packetLength = MimeTypes.APPLICATION_MP4CEA608.equals(mimeType) ? 2 : 3;
     switch (accessibilityChannel) {
       case 3:
       case 4:
@@ -238,8 +243,9 @@ public final class Cea608Decoder extends CeaDecoder {
     ccData.reset(inputBuffer.data.array(), inputBuffer.data.limit());
     boolean captionDataProcessed = false;
     boolean isRepeatableControl = false;
-    while (ccData.bytesLeft() > 0) {
-      byte ccDataHeader = (byte) ccData.readUnsignedByte();
+    while (ccData.bytesLeft() >= packetLength) {
+      byte ccDataHeader = packetLength == 2 ? CC_IMPLICIT_DATA_HEADER
+          : (byte) ccData.readUnsignedByte();
       byte ccData1 = (byte) (ccData.readUnsignedByte() & 0x7F);
       byte ccData2 = (byte) (ccData.readUnsignedByte() & 0x7F);
 

library/src/main/java/com/google/android/exoplayer2/util/MimeTypes.java

@@ -70,7 +70,8 @@ public final class MimeTypes {
   public static final String APPLICATION_TTML = BASE_TYPE_APPLICATION + "/ttml+xml";
   public static final String APPLICATION_M3U8 = BASE_TYPE_APPLICATION + "/x-mpegURL";
   public static final String APPLICATION_TX3G = BASE_TYPE_APPLICATION + "/x-quicktime-tx3g";
-  public static final String APPLICATION_MP4VTT = BASE_TYPE_APPLICATION + "/x-mp4vtt";
+  public static final String APPLICATION_MP4VTT = BASE_TYPE_APPLICATION + "/x-mp4-vtt";
+  public static final String APPLICATION_MP4CEA608 = BASE_TYPE_APPLICATION + "/x-mp4-cea-608";
   public static final String APPLICATION_RAWCC = BASE_TYPE_APPLICATION + "/x-rawcc";
   public static final String APPLICATION_VOBSUB = BASE_TYPE_APPLICATION + "/vobsub";
   public static final String APPLICATION_PGS = BASE_TYPE_APPLICATION + "/pgs";