Taken with a Canon 550D through a Sigma 150-500mm at 500mm. The movie was captured using the 640x480 7.2x crop mode.

It's cropping from the native sensor resolution of 5184x3456 pixels, which is obviously much higher than 1920x1080 pixels. So cropping a 640x480 pixel area from the native sensor resolution results in a 7.2x magnification (vertically). People seem to forget that even in full HD mode the camera is using the whole sensor and therefore interpolating the pixels down. This is where the new crop factor comes from.

3456 / 480 = 7.2 This is a crop NOT a digital zoom like uscaling a DVD to HD is for example.