What I really want to do is to export all frames from a movie file as image files, apply a couple of filters to all of them in Photoshop, and then join them all again into a movie file. I already figured out the first two parts (big thanks to the people on these forums that helped me), but I don't know how to join the images again after I finish with them in Photoshop. Any help?
Since you are asking this on a Director forum, I will assume you want a Director solution. You can make a new movie, set to the size and frame rate you want, then add your images to it, one per frame. Then you can go to File, Export... and set the Format to Quicktime. This will render the movie as a mov file which you can recompress using one of many free/shareware programs to make it whatever file format you want.
Of course, a much better thing to do would be to open your original animation in a program like After Effects and add your filters there. It allows most of the same filters that Photoshop has, and wouldn't require as many steps.
I guess I was so stuck looking for a difficult solution that I totally forgot to check if there might be some software that could do the same job more easy and more quickly
Thanks for your advice, bro, I appreciate it!