Paul Grogan of "Gaming Rules!" will be making the official how-to-play videos for Tainted Grail.
So far, he has a walkthrough of the tutorial, which is 4 pages long and designed as a solo play with Beor. It steps through the setup, travel, location actions, a few turns of combat, a few turns of diplomacy, etc. All steps are printed, so you learn by following the directions (for instance, it'll tell you which cards to play and when during the combat/diplomacy encounters). There are no spoilers for the main storyline campaign in the tutorial: Tutorial
Full rules video will be available at a later time (estimated early 2020).