The computer is a 2015 Macbook Pro 13″ with 2.7GHz Intel Core i5, so not outrageous but definitely good enough…
The video I’m combining it with 1064 by 768, fairly low quality. It’s impossible to say whether it does or doesn’t play well because of the nature of the video – it’s a recording to a static powerpoint presentation, so nothing really needs to ‘move’ smoothly. The frame rate on this video is something like 4. I can’t imagine this video is the problem.
Also when I export the animation straight from After Effects, the resulting video plays completely smoothly. It’s only when I try and put it into Premiere Pro and export it from there that I have a problem…