Because 말했지? doesn't have subject, it might mean "Didn't I tell you?" or might mean "Did you tell it(to someone?)" "This video is so perfect! I can't stop watch it again and again!" --> "이 비디오(영화) 꽤 괜찮네! 계속 보게 !"

it literally means "I told you" or even more informally "told ya!" if you wanna say it informally, it would be: "이 비디오 완전 대박이야, 계속 보고 있어!"