It is so hard! I always feel bad since they don't leave for a couple days so put food in with them and water close. Then mine will stay in the coop with the babies for another few days so have food and water in there for them.
1 is either a quitter, clear or early on. Not enough of the egg is filled. 2,3, and 4 looked good. 5 is clear, 6 I see veins but not filled enough to be day 18,. 7 is hard to tell but may be good, 8 is alive but again looks earlier than day 18. And 9 is hard to tell but doesn't look like...
I agree on all this. 1 and 6 look clear like they never developed. If in person you don't see veins, at this stage veins and a good size dark spot should be visible.
Going to rewatch the video too.
I don't have time to watch the full video but you want to candle through the air cell. At day 12-15 you should see really good veins. and you will see the chick moving around. I will try to find pics of mine from around that time to see if I can help you out