Below is a link to a video on the Albo Kali Silat website. The video is quite long, running about 20 minutes. The reason for the length is that it covers and explains quite a number of basic topics involved in working unarmed versus a knife wielding attacker, including movement, bridging, trapping, sensitivity drills, and how the knife moves. This is very basic material that I realized I had never committed to video. Hopefully some here will find this of use or interest:
http://www.albokalisilat.org/unarmed_against_knife.html