Is there a way to run a pre rendered image sequence back through the compositor without having to re-render?
Sure, that happens automatically. As Input use an Image Sequence node with your rendered frames. Do your compositing and Render (you can render directly as video now, if you want). It will have to go through all the frames of course, but it only renders the compositing, so that goes super fast. You don’t need to change the Cycles Samples, because it doesn’t use them, but I would turn of the Denoising, just to be sure (don’t know if it would be used, but it has already been denoised, so…).
