Adaptive Group of Pictures (GOP) is helpful for increasing the efficiency of video encoding by taking account of
characteristics of video content. This paper proposes a method for adaptive GOP structure selection for video encoding
based on motion coherence, which extracts key frames according to motion acceleration, and assigns coding type for
each key and non-key frame correspondingly. Motion deviation is then used instead of motion magnitude in the selection
of the number of B frames. Experimental results show that the proposed method for adaptive GOP structure selection
achieves performance gain of 0.2-1dB over the fixed GOP, and has the advantage of better transmission resilience.
Moreover, this method can be used in real-time video coding due to its low complexity.
Building on the argument that the change of motion states attracts more attention than the motion itself, this letter develops a novel method for key-frame extraction based on motion acceleration vectors. Different from the traditional methods using maximal or minimal motion energy, the proposed method uses the change of motion states, in magnitude and phase, of the main moving objects as the metric for key-frame extraction. Experimental results show that although similar objective performance is achieved by using the proposed method to that achieved with a widely used method based on motion energy, the key frames extracted by the proposed method are more consistent with human perception.