Nothing about the video is actually inconsistent with birds. The problem is that people make a bunch of assumptions that prematurely rule-out birds, and they're wrong to do so. The misleading & self-sabotaging assumptions usually go as follows:
1- Birds wouldn't be flying that fast (people underestimate the speed birds can achieve and often people are assuming they're higher and further away than the actually are)
2- The formation would change more (Birds can keep a very rigid formation sometimes for a long period. Sometimes they drift around, sometimes they don't)
3- The objects are emitting their own light (birds reflect light more than people realize and this is accentuated all the more on IR/night-vision cams)
All the vids I'll share below are birds.
High speed
This one was infamous at the time it first surfaced in 2008. Many assumed it to be black tech, maybe alien, but definitely an aircraft of some sort. Its birds. Watch how the formation changes subtly, but it absolutely changes. Its not a solid craft. Its birds.
Skip to about halfway through this clip to see one almost identical to the OP video. Same rules apply: Its not actually too fast for birds. They keep a tight formation, but so what.. Birds can do that. So nothing about it is actually inconsistent with birds.
Another tight formation here. As we can see from the video title ("Triangular shape UFO"), this sort of video fools a lot of people, even seasoned photographers.
This one is great. Obviously birds.. but notice how the formation holds its shape relatively well. Still birds though. When we zoom in we can even see some flapping.
We can see the flapping in this video also.. And yet its still been misidentified as a "V-shaped UFO caught on camera" (that's the title of the video).
In summary: Nothing about the OP video is inconsistent with birds. Lots of people make the mistake of prematurely ruling birds out due to the reasons I've already explained above. Studying known videos of birds eventually leads one to witness all the things seen in vids of birds misidentified as UFOs, i.e. They move faster than expected. They sometimes appear self-illuminated but they're actually just reflecting light. They can often hold a tight consistent formation giving the appearance of a solid object when in fact its just birds doing what birds do