My wonderful wife took two videos of my most recent 5K. This is the one in which I was really hoping for 19:59 or less and got 21:05 by my watch (official time not posted yet). The first video is at the start:
From these videos I came to two conclusions:
1. My suspicion was correct, at least part of my coming up short was due to starting off faster than I should have. My goal time would have put me at a 6:25 pace. My first mile was in 6:18, which if I had maintained that throughout would have put me at 19:34 for the race, 25 seconds faster than what I was shooting for.
2. I'm pretty happy with my running form.