how to build a Portable hand held Video recorder and player with auto playback

[0john0]

Hello, I'm a newbie. I can use some help to guide as I attempt to research and build as I go.

A want to build a small device no larger than say 4"x6"x1". 

It's function is to temporarily record video of any source (tv, computer, cam etc) for a user specified period of time. From seconds to minutes. 

It retains the recording in RAM until its scheduled time to playback.  The RAM is then freed to continue recording the streaming video.

It's basically a video delay switch box.   

This box would have a control to input the length to delay the playback from 0 to 5minutes.

I making this with a friend for a magic act. 

I guess I would need:
a micro controller to program what to do with the video stream data, where to store it, respond to the time delay input.
need some kind of driver for the video(?)
an input board that would allow inout of the time number (playback delay). Dial or digital etc.
RAM large enough to record 6 minutes of 4K video stream . My guess is 2 Gigs of RAM

I'll take one step at a time and practice with simple steps. First step tp practice is to build a simple video inputs to record and an output to play.

Thanks in advance. I am sure that any comments i get will lead me to think and act on making something.

Cheers~ John