How to add videos onto each other (IPhone)?

I've found 2 apps that add videos onto to each other but when I want to save to my camera roll it always says
"This will only save 30 seconds of your video"
Any apps you guys know of that is free and saves the WHOLE video?

You might just have to do it on a computer. I know iPhones have limitations on the length of video you can send. Would probably be easier on a computer too