Subtract(clip clip1, clip clip2)
Show the difference between two clips, and make the difference blatantly obvious:
Show the difference between adjacent frames:
About offset of luma range
For YUV formats the valid Y range is 16-235, and Subtract takes this into account. This means that the following script
...will result in a "50% grey" clip with luma=126.
If you require a mathematically correct subtract function for 0-255 RGB or YUV data, use Overlay:...which results in a "50% grey" clip with luma=128.