docs: private void addMetadataProviderForMedia(String key, MetadataProvider provider) {
          if (!metadataProviders.containsKey(key)) {
              metadataProviders.put(key, Collections.newSetFromMap(new ConcurrentHashMap<MetadataProvider, Boolean>()));
          }
          Set<MetadataProvider> providers = metadataProviders.get(key);
          providers.add(provider);
      }