Performance and complexity analysis of rate-constrained motion estimation in MPEG-4

Motion estimation constitutes a critical part in video coding since it is computationally expensive and has a substantial impact on the resulting image quality. A very efficient method to estimate motion is through adding a rate constraint for coding of the motion vectors into the estimation process. In this paper we analyze the performance of this approach in the emerging MPEG-4 standard, considering frame- as well as object-based video sequences. The investigations show that rate constrained motion estimation generally offers significant gains in coding efficiency which, however, depend on the shape of the object coded. Complexity measurements further show that a rate constraint imposes only a marginal computational overhead, thus making this approach a useful amendment for an MPEG-4 coder.