For some reason, out of the box the Logitech c920 has choppy video but to fix that on Ubuntu 15.04, run the following:
sudo apt-get install dov4l dv4l libv4l-0 libv4l-dev libv4lconvert0 libvideo-capture-v4l-perl qv4l2 v4l-conf v4l-utils v4l2loopback-dkms v4l2loopback-source v4l2ucp