Reverse video instantly like in Snapchat

Hi,
I’ve googled a lot about reversing videos but couldn’t find what I wanted. It seems like it is very complex, at least years ago, since most of the discussions about this are old. 
But still all the free software for reversing videos isn’t really good and it takes some time.
So how does Snapchat reverse videos instantly? You just record a video and by swiping right you get to the reverse function, which lets you see the video reversed immediately. I’d love to have this possibility in my project. Can anyone help me?