code: function checkFrames(frames) {
              if (!frames[0]) {
                  postMessage({
                      error: 'Something went wrong. Maybe WebP format is not supported in the current browser.'
                  });
                  return;
              }
  
              var width = frames[0].width,
                  height = frames[0].height,
                  duration = frames[0].duration;
  
              for (var i = 1; i < frames.length; i++) {
                  duration += frames[i].duration;
              }
              return {
                  duration: duration,
                  width: width,
                  height: height
              };
          }
docs: sums the lengths of all the frames and gets the duration