It is just that iMovie doesn't like my shots taken at Disney. Other tapes are all OK whenever it comes to those taken at Disney the CPU load will increase as well as RAM used.
The CPU was getting hot and the fan worked very hard as well
It crashed again and on restarting it looks OK again
For other tapes it looked like this while importing, there were CPU load spikes but overall the RAM used was very stable.
I think it may be a sticky tapes that caused the problem.