Steps to get a thumbnail

GetThumbnail.java

@Override
public void getThumbnail(int index, final ResultCallback callback) {
  // Step 1. Get position from the index.
   long position = getSeekPositions()[index];

   // Step 2. Retrieve thumbnail in the background to not block the UI thread.
   retrieveThumbnailForPosition(position, index, (bitmap) -> {
       // Step 3. Return the thumbnail to be presented in the UI.
       callback.onThumbnailLoaded(bitmap, index);
   });
}