It is a little hard to see his conformation and/or action in the video accurately simply because of the distance and the limited quality on many of the shots. From what I CAN see, he looks like a good mover and I'm not seeing any glaring faults that would automatically scream NO ENDURANCE! lol Arabians are traditionally smaller horses, but in todays equine market buyers are demanding taller Arabs, which is a disservice to the breed. Arabs aren't supposed to be big, that is part of the alure (sp) of the breed. The plus to a larger Arab is that you should have a longer stride which can be beneficial in an endurance event. Notice I said "should" and "can". Small Arabs can do just as well if the rider knows how to help the horse use its assets to the best advantage.
The other thing most people don't stop to consider is that when a horse is running around at play, you are not seeing accurate movement that would be expected of a horse under saddle in a show or endurance environment. Additionally, a horse alone in his own environment may behave vastly different from the way he will behave in a show or endurance enviromnent - then again he may not. It depends on the horse.
I don't see anything in his breeding to suggest that he won't make a good endurance horse - on the contrary. Many of the lines he has in his pedigree are common lines I've seen in a lot of good endurance horses. One thing to keep in mind about endurance is that a horse cut out to do a 50 mile ride may not be cut out to do a 100 mile ride and the reverse is also true. The 25 and 30 mile LD and CTR rides are also vastly different from the 50, 75 and 100 mile rides. This is not just because of the distance. Because of the metabolics involved in a shorter ride, it can be much more difficult for a horse to complete a shorter ride.
How long has he been under saddle? Most endurance horses aren't even started under saddle until at least 3-4 years old - preferably 4. He has to have a good foundation of groundwork as well as being proficient in walk, trot, canter transitions. Accurate transitions are what will keep you alive during your endurance event. Like training for any discipline, you want to make progress, but don't overwhelm him. Endurance is a demanding, yet rewarding sport. You will have to have the dedication to train for it daily, and not just a few laps around the arena. You have to get out on the trails and on different footing. A minimum riding session should be at least an hour.
Nutrition is also a consideration. An endurance horse is going to need to have a higher protein and fat content to help their muscles recover quickly and a bit of fat makes a good energy reserve. Naturally, you need some carbs in there too, but the complex carbs are going to provide a better source of available energy than the simple carbs because the complex carbs don't burn as fast as the simple.
It also may be necessary to put shoes on his front feet, or easy boots. Even if he has the best hooves in the world, you want to protect his soles from the hazards on the trail that will likely bruise his unprotected sole.
There are some great resources for you to check out: SEDRA - www.distanceriding.org
; AERC – www.aerc.org
; and of course FEI - Welcome To FEI Fédération Equestre Internationale
I hope I have answered some of your questions without overwhelming you. I'd be happy to help out more if you want to PM me.
Best of luck to you and your horse!