iMovie crashing during optimization

This is because of a hardware overload. The best solution is to close any other programs by double clicking on the home button. then a bar of previously used applications will pop up. Place and hold your finger on one of the widgets until they all start shaking. then one by one delete all of the app history by clicking the red button on the top corner of the widget. This should work, however if it doesnt, you can then try restarting the phone.

Also, just a bit of a little more infomation, when the iPhone 5S comes out, with an A7 Chip, the A5 Chip inside the iPhone 4S will render more obsolete. When iPhone 5S comes out with updated Chip technology, the iPhone 4S will not be able to handle aggressive programs like iMovie much better. I suggest you cease updating your applications in order to preserve major operating performance.

Let me know if you have any other questions.

Thanks,

Allen