In the OP's video, it looks like the fire is magically coming out of thin air... it'd be hard to do the animation style I linked at the distance in OP's video though, so I'm not sure how they could better animate a solid fuel rocket
Aha! Very nice! So this is why solid fuel boosters are ejected before they’ve burned out - because they will eventually burn out to the edges of the tube and the whole thing will start to glow?
so yeah it is all burning at the same time
In the OP's video, it looks like the fire is magically coming out of thin air... it'd be hard to do the animation style I linked at the distance in OP's video though, so I'm not sure how they could better animate a solid fuel rocket