I/P/B Frame Type Decision by Collinearity of Displacements (WA-P5)

Author(s) : Adriana Dumitras (Apple Computer, USA) Barry G. Haskell (Apple Computer, USA)

Abstract : State-of-art encoders in real life applications typically select the number of B frames to be coded between each I or P picture to be equal to one or two. The few research works that have addressed the problem of encoder optimization by frame type decision rely on measures of motion magnitude and amount to select the number of B frames. In contrast to such solutions, in this paper we advocate the idea of motion similarity in terms of speed and direction as the basis for deciding how many B frames to code between any two stored pictures. Such similarity is evaluated by the colinearity of the displacements in successive frames. Experimental results using our decision method and an H.264 compliant codec show that the bit rates of the compressed streams and the peak signal-to-noise ratios of the decoded sequences are, on average, near-optimal and optimal (respectively) with respect to those obtained using the optimal fixed number of B frames for each sequence. Moreover, our method provides a simple form of temporal scalability and can be employed in any coding system that makes use of I, P and B frames.

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