My time had run out so I simplified the sequence by deleting effects and still images and exporting the video. When it became less heavy with effects etc the video exported without freezing or crashing.
I used a iMac,
processor: 2.8GHz Intel Core i7,
Memory: 8G 1333 MHz DDR3 memory
Graphics: AMD Radeon HD 6770m 512MB
Running on OS X 10.9.5