First pass at text track selection, mostly complete

ios/RCTVideo.m

@@ -40,6 +40,7 @@ static NSString *const timedMetadata = @"timedMetadata";
   BOOL _muted;
   BOOL _paused;
   BOOL _repeat;
+  NSDictionary * _selectedTextTrack;
   BOOL _playbackStalled;
   BOOL _playInBackground;
   BOOL _playWhenInactive;
@@ -625,6 +626,7 @@ static NSString *const timedMetadata = @"timedMetadata";
     [_player setMuted:NO];
   }
 
+  [self setSelectedTextTrack:_selectedTextTrack];
   [self setResizeMode:_resizeMode];
   [self setRepeat:_repeat];
   [self setPaused:_paused];
@@ -635,6 +637,50 @@ static NSString *const timedMetadata = @"timedMetadata";
   _repeat = repeat;
 }
 
+- (void)setSelectedTextTrack:(NSDictionary *)selectedTextTrack {
+  _selectedTextTrack = selectedTextTrack;
+  NSString *type = selectedTextTrack[@"type"];
+
+  AVMediaSelectionGroup *group = [_player.currentItem.asset
+                                  mediaSelectionGroupForMediaCharacteristic:AVMediaCharacteristicLegible];
+  
+  AVMediaSelectionOption *option;
+  if ([type isEqualToString:@"disabled"]) {
+    // Do nothing. We want to ensure option is nil
+  } else if ([type isEqualToString:@"language"] || [type isEqualToString:@"title"]) {
+    NSString *value = selectedTextTrack[@"value"];
+    for (int i = 0; i < group.options.count; ++i) {
+      AVMediaSelectionOption *currentOption = [group.options objectAtIndex:i];
+      NSString *optionValue;
+      if ([type isEqualToString:@"language"]) {
+        optionValue = [currentOption extendedLanguageTag];
+      } else {
+        optionValue = [[[currentOption commonMetadata]
+                        valueForKey:@"value"]
+                       objectAtIndex:0];
+      }
+      if ([value isEqualToString:optionValue]) {
+        option = currentOption;
+        break;
+      }
+    }
+  } else if ([type isEqualToString:@"index"]) {
+    if ([selectedTextTrack[@"value"] isKindOfClass:[NSNumber class]]) {
+      int index = [selectedTextTrack[@"value"] intValue];
+      if (group.options.count > index) {
+        option = [group.options objectAtIndex:index];
+      }
+    }
+  } else { // default. invalid type or "system"
+    // _player.appliesMediaSelectionCriteriaAutomatically = YES;
+    return;
+  }
+  
+  // If a match isn't found, option will be nil and text tracks will be disabled
+  // _player.appliesMediaSelectionCriteriaAutomatically = NO;
+  [_player.currentItem selectMediaOption:option inMediaSelectionGroup:group];
+}
+
 - (BOOL)getFullscreen
 {
     return _fullscreenPlayerPresented;

ios/RCTVideoManager.m

@@ -22,6 +22,7 @@ RCT_EXPORT_MODULE();
 RCT_EXPORT_VIEW_PROPERTY(src, NSDictionary);
 RCT_EXPORT_VIEW_PROPERTY(resizeMode, NSString);
 RCT_EXPORT_VIEW_PROPERTY(repeat, BOOL);
+RCT_EXPORT_VIEW_PROPERTY(selectedTextTrack, NSDictionary);
 RCT_EXPORT_VIEW_PROPERTY(paused, BOOL);
 RCT_EXPORT_VIEW_PROPERTY(muted, BOOL);
 RCT_EXPORT_VIEW_PROPERTY(controls, BOOL);