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One of the creatures I’m most worried about meeting camping or hiking is a moose. If they had a moose’s temperament they would have been one of the most terrifying things to walk the earth. They would also probably be getting hammered off fermented prehistoric fruit

That and more really. You could use it to do a green screen effect, but you can also use it to adjust color balance, brightness or do weirder things like swapping values between colors. It gets really crazy when you are working with full video because the time of the current frame is also available to be incorporated, so you can even do animated effects.

Another powerful filter is the convolve filter. That allows you to apply matrix transformations, which can for example be used to apply a homography matrix and adjust a videos perspective.

Well for instance you can use it to apply tranparencys or other effects using the geq filter. It applies a formula to every pixel in the input and can adjust alpha, rgb values, and gamma. You can also use conditionals in your formula and have access to the current pixels location and value, so you can apply your transforms only to specific regions if you want, or do an adjustment keyed only to a specific color.

Ffmpeg has been such cool software to learn. Simple filter chains can do incredible things