With the version of Windows Movie Maker that I use, I think I can pixelate a video image (it's one of the effects) but maybe not just a certain part of that image, like a person's face. About changing people's voices, you may be able to make the voice faster or slower if you use the speed up or slow down effect in a video segment with the person's voice. And you can adjust the volume. But that might be about it. I'm sorry if I couldn't be of more help.