I just downloaded one called Seconds, which is mostly intended for circuit training (e.g. 30 second exercise, 10 second break, etc) but the times and exercises can be customized. Custom workouts can only be saved and reused later if you get the paid version, which I haven't done. Not sure this is really what you're looking for, though. There are also productivity apps that track activities (Way of Life, Fig, Chains, SimpleGoals are the ones I've played with a bit) but I don't think you can add video to them.