Iphone as wireless camera monitor? - 1

Asked this once before, didn't receive an actual answer.

I'm an independent filmmaker and have recently helped out at a larger scale film shoot downtown. I noticed that a producer had her iphone out and it had a live monitor feed of what was being shot! When i look it up online people say it isn't possible. But I saw it with my eyeballs, so it is.

I know the new GoPros have a Wi-Fi remote app feature, but i'm not talking about that.

I have a Canon DSLR camera.

How does this work and how can I do this?

To clarify… I was not able to speak to the producer that day, and I want to know how to do this for my own films with my dslr (which has a mini hdmi output)

It you post this at uglyhedgehogs.com or digitalphotraghyschool.com I'm sure those guys that do that will gladly tell you how. Sorry couldn't give you clickable links as outside on my cell pho, but I do think those are good urls.