code: public static Bitmap getVideoThumbnail(String videoPath){
          MediaMetadataRetriever mmr = new MediaMetadataRetriever();
          mmr.setDataSource(videoPath);
          return mmr.getFrameAtTime();
      }
docs: Get a thumbnail bitmap for a given video
  
  @param videoPath     the path to the video
  @return              the thumbnail of the video, or null