code: function getFilterGraphFlags(sizeObj) {
          if (sizeObj.filter && typeof sizeObj.filter === 'string') {
              return sizeObj.filter;
          } else {
              return 'scale='+sizeObj.width+':trunc(ow/a/2)*2';
          }
      }
docs: Build filter graph flag, giving preference to a custom filter. If none, construct the filter with the given width. http://ffmpeg.org/ffmpeg-filters.html#Filtering-Introduction