^
If you zip a movie, it will only halve in size. You can .rar like 11 movies and make it a lot smaller.
It all depends on the compression algorithms used. Videos also don't compress very well:

Compressing data isn't just taking the existing data and cramming it into smaller space with the only drawback of you needing to decompress the data before you can use it. It's much more complex than that.
Yes the .7z native compression algorithm actually made the file 4 MB larger.