There are digital filters that add film grain effects, but nothing compares to the real thing. These free film grain overlays are actual footage shot on 8mm film, captured optically for 30 seconds, so you won't sense repetitions or patterns – not the short snippets you'll find elsewhere.
The download includes four 30-second overlays in full HD (1.2GB) - low grain, medium grain, high grain, plus a hand-developed stock that adds dust and scratches.