Los Santos' gone crazy! Everybody shoots and fights against everybody, including you. That's what happens if you use the Pedestrian Riot Mod on GTA V, PC only!
You can get it here: https://www.gta5-mods.com/scripts/pedestrian-riot
I also used BulletCam script when i was using the sniper (from 6:25): https://www.gta5-mods.com/scripts/bulletcam
...and if you want to check screenshots from this video with better quality: http://imgur.com/a/uYjQX