This paper presents a new algorithm for determining the optimal MPEG coding strategy in terms of the selection of macroblock coding modes and quantizer scales. In the algorithm proposed in the test model the rate control operates independently from the coding mode selection for each macroblock. The coding mode is decided based only upon the energy of predictive residues. Actually, the two processes of coding mode decision and rate control are intimately related to each other and should be determined jointly in order to achieve optimal coding performance. We formulate the constrained optimization problem and present solutions based upon rate-distortion characteristics, or R(D) curves, for all the macroblocks that compose the picture being coded. Distortion for the entire picture is assumed to be decomposable and expressible as a function of individual macroblock distortions, with this being the objective function to minimize. The determination of the optimal solution is complicated by the MPEG differential encoding of motion vectors and DC coefficients, which introduce dependencies that carry over from macroblock to macroblock for a duration equal to the slice length. As an approximation, a near optimum greedy algorithm is proposed. Once the upper bound in performance is calculated, it can be used to assess how well practical suboptimum methods perform. Finally, such a practical suboptimum algorithm is proposed and evaluated.

The idea of moving picture expert group (MPEG) bitstream scaling relates to altering or scaling the amount of data in a previously compressed MPEG bitstream. The new scaled bitstream conforms to constraints that are not known nor considered when the original preceded bitstream was constructed. Numerous applications for video transmission and storage are being developed based on the MPEG video coding standard. Applications such as video on demand, trick-play track on digital video tape recorders (VTR's) and extended-play recording on VTR's motivate the idea of bitstream scaling. In this paper, we present several bitstream scaling methods for the purpose of reducing the rate of constant bit rate (CBR) encoded bitstreams. The different methods have varying hardware implementation complexity and associated trade-offs in resulting image quality. Simulation results on MPEG test sequences demonstrate the typical performance trade-offs of the methods.

The Moving Picture Expert Group (MPEG) video coding standard has been proposed for a variety of applications for video transmission and storage. Several applications such as video on demand, trick-play track on digital VTRs and extended-play recording VTRs motivate the idea of bitstream scaling which intends to reduce the compressed bitstream size according to the outgoing channel capacity. We propose several methods for implementation of bitstream scaling. The different methods have varying hardware implementation complexity, with each having its own degree of tradeoff between required hardware and resulting image quality.

An algorithm for lost signal restoration in block-based still image and video sequence coding is presented. Problems arising from imperfect transmission of block-coded images result in lost blocks. The resulting image is flawed by the absence of square pixel regions that are notably perceived by human vision, even in real-time video sequences. Error concealment is aimed at masking the effect of missing blocks by use of temporal or spatial interpolation to create a subjectively acceptable approximation to the true error-free image. This paper presents a spatial interpolation algorithm that addresses concealment of lost image blocks using only intra-frame information. It attempts to utilize spatially correlated edge information from a large local neighborhood of surrounding pixels to restore missing blocks. The algorithm is a Gerchberg (1974) type spatial domain/spectral domain constraint-satisfying iterative process, and may be viewed as an alternating projections onto convex sets method.