Video throttling is an artificial constraint of the number of impressions per hour. Google partner inventory has a throttling threshold to protect publishers from ads with a high error rate. New video ads are initially throttled because no error rate yet exists.
Video Throttling occurs when: Error Rate > Fixed Threshold
Error Rate = number of errors / number of auctions won
Error Rate = number of errors / number of auctions won
If the error rate improves, throttling is removed. Video throttling implementation is subject to change.