Video Footage showing devices on a still background but featuring videos in screens

My website allows either video or video files (WEBM, MP4) to be shown as the header to my homepage and I am trying to do something very specific. I would like a short video clip (30-40 seconds) which features the following (if possible): - still background (so it effectively looks like a picture) - 10-15 seconds overlay images of a Mac, then iPad, then iPhone to feature on the righthand side of the above image - for each of the above devices to feature video footage on their screens of our online system The purpose of this video is to demonstrate how our system works on the devices, but as it is the head of the website, it will also be featuring some text and buttons overlaying the final video on the left hand side (hence the video action needs to be on the right hand side with a still image). Please see the attached image for an example. There is a still image in the background, and I will overlay text on the left hand side. I would like an iMac type device to be on the right handside, as if working our online system, before fading out to show a iPad showing our system and the iPhone showing our system. Not, the iMac, iPad and iPhone must all be showing a moving image of our system as if it looks as though someone is using it live.