There is also Gloobus for preview. Just follow the steps below and you do not even need to restart Nautilus or do anything. Install PPA, Update, install packages, done.
sudo add-apt-repository ppa:gloobus-dev/gloobus-preview
sudo apt-get update
sudo apt-get install gloobus-preview gloobus-sushi
Gloobus is an alternative to Sushi (Which I find much better since it supports a couple of friendly options) and you can preview Avi files, MKV files, Video files in general, sound files in general, text, pdf, etc... Just press space and PREVIEW. Press space again and preview off. Also you can start previwing a file and use your keyboard arrows to move to another file for preview.
If you are using 13.04+ the following is the install command line:
sudo apt-get install gloobus-preview