Someone did it better than me so check it out here: https://github.com/Filarius/video2video
a simple script addon for https://github.com/AUTOMATIC1111/stable-diffusion-webui takes video as input, runs it through img2img and then outputs a video with the generated frames.
1. Download FFMPEG just put the ffmpeg.exe and the ffprobe.exe in the stable-diffusion-webui folder or install it like shown here. Edit: Make sure you have ffprobe as well with either method mentioned.
3. start/restart the webui and on the img2img tab you will now have vid2vid in the scripts dropdown.
Generally i would advise you to play around with different settings, maybe a set seed, more or less denoising, more or less sampling steps etc, since the output quality can differ based on the input video, resolution, prompt and all that.