NOTE this only works with videos that have 'play' and 'pause' controls as it crops the left and right edges of the video and moves the Vimeo controls off screen.

This is a method of converting aspect ratios of responsive videos using ONLY CSS and still keep the converted videos responsive. No need to use video conversion software or jQuery/javascript.

The CSS makes full use of the calc() function to calculate the width, height and offset for the new aspect ratio and will work in all modern browsers and operating systems.

There is a further benefit, using this method, in that you can manipulate the 'offset left' (cropped) area to keep video interest centered.