Fifteen to thirty seconds is the optimum length of a video clip. This may sound short, but it is about the same length as a TV commercial. It's no accident that commercials are this length. Much research has gone into determining the duration of viewer attention span. Anything longer than forty-five seconds and you risk having your prospect's eyes glaze over.
Impact is what is remembered.
The message is important, but who is saying it is key. The most effective video clip testimonials show subjects being natural and conversational, but they must clearly communicate a specific message. You may have the same client talking about several issues. One strong statement per clip works best. For example, one clip may be about a problem your company solved for them, or another may explain how your service saved them money.