Here are links to the few Zentangle demonstration videos on the internet. I don't like to be negative, but I'll advise you that most of what is billed as 'zentangle' instruction on YouTube, simply is not Zentangle. Fortunately, more videos are appearing from people who do understand Zentangle. (That's a disclaimer; I'm probably missing some!)
AURAKNOT - an 'official' tangle from Rick Roberts and Maria Thomas
BETWEED - an 'official' tangle from Rick Roberts and Maria Thomas
COIL - from Sue Jacobs, CZT
DIVA DANCE - created by Maria Thomas and Rick Roberts for Laura Harms, CZT, in honor of the Diva's 100th weekly Zentangle challenge, and demonstrated by Laura.
FUNGEES - from Leslie Crumpler, CZT
MOOKA - an 'official' tangle from Maria Thomas
PEANUCKLE - Cris Letourneau, CZT, demonstrates Molly Hollibaugh's tangle Peanuckle.
PURK - Maria Thomas demonstrates her 'official' tangle at a CHA convention.
Two short, charming, and delightful videos by Zach, a Texas design student.
"Zentangle in Motion" - a three minute video of every stroke during the creation of a Zentangle tile - 947 strokes in all! Watch it here.
"Zentangle in Motion 2" - over 2000 images of the development of another Zentangle tile. Watch the three minute video here.