Really? Are you sure you read my post correctly? I didn't say 4K video, or even 2K. I said 1080p.
I've been editing 720p video on an iMac with only 1GB of memory for about 6 years now, and everything has always worked just fine.
720 x 2 = 1440 (obviously a larger number than 1080), therefore I would have guessed 2GB of memory is fine, and 3GB is more than enough... I'm not claiming to be a computer expert though.
(1920x1080) / (1280x720) = 2.25, that's much more pixels than what you believe..
If I want to edit 1080p video comfortably on iMac, how much memory should the iMac have? Thank you.