I think that they are CX. Mine second batch was in a tractor and they are definitely more active and smaller than my first batch. We are actually getting ready to butcher tomorrow at 10 weeks and have birds about the same size as our last batch butchered at 8 weeks.
They could be white rocks. You'll know for sure when they are about 8 weeks old. If Cornish X, when you pick them up, they'll feel like bowling balls! They also have a lot of feathers for Cornish X. The ones I had were very sparsly feathered.
I have to second guess myself after the later pics and video. I'm guessing they're CX that heven't neen fed nearly enough, though to be completely honest I can't understand why. I have 10 week old CX pullets on tightly rationed diets to get them to breeding age. They move as well or better as those shown, and one has even flown over a 4 foot fence to get to another pen.
Here's some pictures of some of my 21 CX pullets at 10 weeks old, weighing an average of 4 lbs, though there's about 3/4 lb difference between the smallest and largest, so I've included pictures of both. [5 lost to an owl, the rest in excellent health]
ETA: The dirty feathers are from a damp sand bathing area they've made for themselves
Could they be straight run Cornish X rather than all males? I know when we did males we got huge birds really quickly but when we did straight run it took them a lot longer to grow than the boys.
Oh they are straight run! Which is why we were going to leave them to 10 weeks to get some larger, some smaller.
Before letting them out they were getting grass/bugs under the tractor moved 3x a day (at least) plus ... I didn't measure it but at least 2KG of feed twice a day. (going to go measure it now)
There are 45 of them so there are many more then just in the video (those are just the guys who came over to see what I had). They all look a little different.
Some look more like the white rocks, some look more like the CX, some look more like the leghorns - which leads me to believe they are a meat mix.
I had the same problem with my Cornish X this batch as well. I ordered straight run and they just aren't growing the same as when I get all boys. Not sure if the girls just look more like layers or what.