Fixed the Mp4 embedded WebVTT playback

Issue: #1185
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=117136646

library/src/main/java/com/google/android/exoplayer/dash/mpd/MediaPresentationDescriptionParser.java

@@ -629,11 +629,14 @@ public class MediaPresentationDescriptionParser extends DefaultHandler
       return getVideoMediaMimeType(codecs);
       return getVideoMediaMimeType(codecs);
     } else if (mimeTypeIsRawText(containerMimeType)) {
     } else if (mimeTypeIsRawText(containerMimeType)) {
       return containerMimeType;
       return containerMimeType;
-    } else if (MimeTypes.APPLICATION_MP4.equals(containerMimeType) && "stpp".equals(codecs)) {
-      return MimeTypes.APPLICATION_TTML;
-    } else {
-      return null;
+    } else if (MimeTypes.APPLICATION_MP4.equals(containerMimeType)) {
+      if ("stpp".equals(codecs)) {
+        return MimeTypes.APPLICATION_TTML;
+      } else if ("wvtt".equals(codecs)) {
+        return MimeTypes.APPLICATION_MP4VTT;
+      }
     }
     }
+    return null;
   }
   }
 
 
   /**
   /**

library/src/main/java/com/google/android/exoplayer/text/TextTrackRenderer.java

@@ -90,7 +90,7 @@ public final class TextTrackRenderer extends SampleSourceTrackRenderer implement
     }
     }
     try {
     try {
       DEFAULT_PARSER_CLASSES.add(
       DEFAULT_PARSER_CLASSES.add(
-          Class.forName("com.google.android.exoplayer.text.mp4webvtt.Mp4WebvttParser")
+          Class.forName("com.google.android.exoplayer.text.webvtt.Mp4WebvttParser")
               .asSubclass(SubtitleParser.class));
               .asSubclass(SubtitleParser.class));
     } catch (ClassNotFoundException e) {
     } catch (ClassNotFoundException e) {
       // Parser not found.
       // Parser not found.