Videos won't compress much, if any.
To elaborate on that. Certain files already have their own compression algorithm implemented (such as jpg, mpg, mp3, etc.). So when you try to compress these files it doesn't work because there is nothing more to compress and sometimes it will use more space because of the file information that has to be stored in the archive.
So there is no easy way to compress video files because they are already compressed. The only way you could probably save space is if you convert them to a format that has a better compression ratio, but then you will of coarse, loose quality.
