No video, no photograph, no recording. Every flame is drawn and every crack is made on the spot.
The flame is a particle fire and nothing else. Along the top of the logs, little
parcels of hot gas are released, given an upward push and a sideways drift, and then curled by
a slow-moving field so the column wanders instead of standing still. Each one is drawn as a
soft blob added to what is already there — globalCompositeOperation = 'lighter'
— which is why overlapping flames go white-hot in the middle without anybody painting a
white middle. Its colour is read off its own age, from pale yellow through orange to a dull red
and then to smoke, because that is what a cooling parcel of gas actually does.
The crackle is Web Audio, not a loop. A crack is a few milliseconds of noise through a sharp resonant filter, struck at a random rate; a pop is the same thing louder with a low thump under it; and beneath both sits a filtered rumble that gets louder and broader as you push the fire up. Turning the logs up makes the cracking busier, because more wood is more to crack. Nothing here is sampled and no audio file is fetched.
Poking it does what poking a fire does — a rush of sparks and a brief flare as the bed is opened up, settling back down after a few seconds on its own.
There is nothing to achieve here. The fire does not go out, the logs do not need replacing, and leaving the tab does not cost you anything.