Is there a filter that looks like youtube compression?

I don't have enough power to use good anti aliasing,but the youtube compression looks kinda good,so is there a filter like that?

You might try Gaussian Blur and Surface Blur, with maybe a touch of Bloom.

SMAA and FXAA are amongst the cheapest possible shaders to use. I can't imagine not having the gpu power to use one of them over a 0.5 pixel gaussian filter.

What exactly is the difference between Gaussian and Surface blur?

Quite literally everything.

Gaussian blur is just a one method to do blur while SurfaceBlur is its own complete shader. The former blurs everything while the latter tries to algorithmically blur only very low detail areas while leaving high details un-touched.