Add saving subtitle track name for MatroskaExtractor

library/extractor/src/main/java/com/google/android/exoplayer2/extractor/mkv/MatroskaExtractor.java

@@ -2139,6 +2139,7 @@ public class MatroskaExtractor implements Extractor {
       Format format =
       Format format =
           formatBuilder
           formatBuilder
               .setId(trackId)
               .setId(trackId)
+              .setLabel(name)
               .setSampleMimeType(mimeType)
               .setSampleMimeType(mimeType)
               .setMaxInputSize(maxInputSize)
               .setMaxInputSize(maxInputSize)
               .setLanguage(language)
               .setLanguage(language)

library/ui/src/main/java/com/google/android/exoplayer2/ui/DefaultTrackNameProvider.java

@@ -48,6 +48,11 @@ public class DefaultTrackNameProvider implements TrackNameProvider {
               buildLanguageOrLabelString(format),
               buildLanguageOrLabelString(format),
               buildAudioChannelString(format),
               buildAudioChannelString(format),
               buildBitrateString(format));
               buildBitrateString(format));
+    } else if (trackType == C.TRACK_TYPE_TEXT) {
+      trackName =
+          joinWithSeparator(
+              buildLabelString(format),
+              buildLanguageString(format));
     } else {
     } else {
       trackName = buildLanguageOrLabelString(format);
       trackName = buildLanguageOrLabelString(format);
     }
     }