Great app setup BUT.... – Veescope Green Screen Full Review

Every time I try to make a green screen video, the video looks "laggy" "glitchy" or "jumpy" and i know it's a "live chroma keying app" but I would like to, be able to use my already shot footage in my photo albums for the green screen. So it would be a cool little update if you guys did add that. I spent like $3 on the app and haven't even used it, cause it wouldn't work. Can you help? I have an iPhone 5 btw
Review by CHEESEonPHILY on Veescope Green Screen Full.