Go to 'go advanced' at bottom of the reply screen.
Select the youtube icon, and just copy-paste the URL of your video directly in there.
I'm assuming you're uploading to a youtube account? You will need that or something similar I think.
W.A. AMATEUR STRONGMAN
Axle clean-press: 100 kgs (220 lbs)
Bench press: 135 kgs (298 lbs) - 1st PL meet 16th October 2011
Deadlift w/Barbell: 180 kgs (397 lbs)
Deadlift w/Hexbar: 225 kgs (496 lbs)
Farmers walk: 240 kgs (530 lbs), 50 feet
Front squat: 100 kgs (220 lbs)
Log clean-press: 100 kgs (220 lbs)
Strict OHP: 85 kgs (187 lbs) 3 reps
Tyre flip: 260 kgs (573 lbs), 100 feet