iMovie hanging during putting the videos

- MacBook Pro,13-inch high-performance notebook with Retina display.

- 8GB SDRAM.

- 128GB of flash storage.

- OS X El Capitan 10.11.3

I Have Problem with iMovie when i use it with the photos its OK , but just start work with the videos the program start hanging and cant watch the videos even with out editing and cant put any editing on the videos.

i tried to but videos with small size but the same thing happens.