Simulate page scroll in keynote

I have a screen in my slide (iMac) and I have a mask (display), the mask image in the display is my website, which is 3000 pixels tall, then mask is 800 pixels tall, what I am trying to do is animate from the top of the page to the bottom, simulating the browser scroll.

My first port of call was magic move, which I have successfully used when not using masks, so essentially when I have two slides of the same image in different position, magic move "Tweens" the frames in between. When trying this with the same image in the mask, it simply fades it, rather than animates it, not really sure why this is, it is like it is not detecting that the position of the image within the mask, just that it has changed.

Is there any way round this?

Solution 1:

I actually figured it out myself. I basically created a transparent PNG of the iMac screen with the display itself transparent, then I placed the website screenshot into keynote and sent to back. Now Magic move works great.