How to make centre cropped image responsive?

Question

Based on an existing answer, I have managed to centre crop an image. I am having trouble making the centre cropped image responsive, though.

Question

Answer 1

Does this Fiddle do the right cropping?

With the following CSS we can maintain the aspect ratio of the container when resizing the window.

width: 640px;
max-width: 100%;
height: 0;
padding-bottom: 50%; // 320px or lower (half of the width)