mw for max-width and mh for max-height. Images are resized automatically in this template and there is no script for it. Actually we used hosted placeholder image link from youtube and vimeo. Their thumbnail image is small size and we need it larger then them that’s why we used mw and mh. For using mw and mh browser catch the actual dimension from their server defined as mw and mh. If your images all are large size like 1920*1080 then you can remove the mw and mh form every image but it will affect your loading time. We suggest to use hosted thumbnail image for video.
Hope this will give you a clear concept.