Scaling down a texture for use in shader

I'm trying to modify an existing example so that I can apply a shader to a recorded video clip. The problem I'm running into is that the camera is capturing at 1280 x 720, but the quad I'm trying to map that texture to is 640 x 480. I can access the texture in my shader, but it's cropping the texture and not scaling it like I want. Any help is appreciated.