I have enabled the html5 video's in Youtube. Whenever I play a video in html5, I get to see weird horizantal lines:
I'm using the latest Google Chrome on Ubuntu 13.04. I've got a Nvidia K1000M graphics card with the latest proprietary drivers installed. How do I fix this issue?
That's known as screen/video tearing. You can try to enable or disable Vertical Sync, or set it to Adaptive.
If you've tried playing videos outside the browser with VLC, Totem and other applications and the problem still remains, I suggest you check this thread: How do I stop video tearing?