1. A computer-implemented process for compressing video data comprising sequential sets of contemporaneous video frames wherein the video frames in a set depict substantially the same scene from different viewpoints, said process comprising: using a computer to perform the following process actions: designating a plurality of keyframes for each set of contemporaneous frames such that no non-keyframe in a set has a viewpoint that is more than a prescribed number of viewpoints away from the viewpoint of at least two designated keyframes; and for each set of contemporaneous video frames in time sequence order, compressing each video frame that is not a keyframe using at least two keyframes which are no more than said prescribed number of viewpoints away from the non-keyframe being compressed as reference frames for a multi-directional spatial prediction compression technique.