Science! This 1000uf 35v Low ESR Capacitor, made by Panasonic, is great for reducing the noise in your setups. Ideal on setups which have little on-board filtering (like a setup using a 4 in 1 ESC), this Panasonic Capacitor will add a ton of filtering might to your setup. The result will be better video, less noise introduced to your Flight Controller, and a setup which overall operates better than a setup without a capacitor.
Solder the capacitor direct to your battery lead, either at the XT60 or, preferably, solder it directly to the primary positive and negative leads where your XT60 pigtail meet your 4-in-1 ESC. Ensure positive and negative are correct.
Link to Oscar Liang Article about capacitors.