Interesting videos. I'm not really able to interpret however. The fight seems to take place in the War of Independence. At that late time at least the British troops should have the most modern fire mode.

This means imho a combination of platoon fire and volley fire. At least this would be true for the Prussian army. I'm not as sure for the British, but I think they used a similar system. With platoon fire it is of course normal that only parts of the line are firing at the same time. But the fire is steady and without pause, contrary to the outdated rank firing.

By no means rank firing was a modern form of firefight in the 18th century. It was the old form, used already in the 1600s. Some armies were bound to this antique form of fire longer than others, f.e. the French. But the Prussians and British f.e. developed platoon fire relatively early. The Prussian army in the middle of the 18th c. used volley fire (meaning that the entire battalion fires at once) in some circumstances too, f.e. from short distance prior to a bajonet charge. Platoon firing from greater distances was however the norm.

I hope CA got it right and platoon firing is in the game.