In conventional bit-rate control, the buffer level is controlled by adapting the quantization step size with a fixed frame rate and spatial resolution. We consider a multidimensional (M-D) bit-rate control where the frame rate, spatial resolution and quantization step size are jointly adapted for buffer control. We introduce a fundamental framework to formalize the description of the M-D buffer-constrained allocation problem. Given a set of operating points on a M-D grid to code a nonstationary source in a buffer-constrained environment, we formulate the optimal solution. The formulation allows a skipped frame to be reconstructed from one coded frame using any temporal interpolation method and is shown to be a generalization of formulations considered in the literature. In the case of intraframe coding, a dynamic programming algorithm is introduced to find the optimal solution. The algorithm allows one to compare operational rate-distortion bounds of the M-D and conventional approaches. We also discuss how a solution can be obtained for the case of interframe coding using the optimal dynamic programming algorithm for intraframe coding by making an independent allocation approximation. We illustrate that the M-D approach can provide bit-rate reductions over 50%. We also show that the M-D approach with limited-lookahead provides a slightly suboptimal solution that consistently outperforms the conventional approach with full-lookahead.

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In a typical MC-DCT encoding scheme, a large portion of the bit rate is used to encode the location and amplitude information of the nonzero quantized DCT coefficients. Therefore efficient encoding of the DCT coefficients is extremely important. In this paper we describe the Joint Position-Dependent Encoding (PDE) approach to encode the DCT coefficients. Joint PDE exploits the variations in statistical properties of the runlengths and amplitudes as a function of position by introducing a set of 2-D codebooks in which each quantized DCT coefficient is assigned to one codebook in the set based on its location. Utilizing an MPEG-2 codec, we compare the bit rates using the joint PDE variable length codes (VLC's) with the bit rates produced by the MPEG-2 VLC's. We also examine how performance is affected by the number of codebooks.

In digital video communications, buffering is required to absorb variations between the source rate and the channel rate. Hence, a bit rate control strategy is necessary to maintain the buffer level. In conventional bit rate control, the buffer level is maintained by adapting the quantization stepsize while the frame rate and spatial resolution remain fixed at levels chosen a priori. This thesis investigates a Multi-Dimensional (M-D) bit rate control where the buffer level is maintained by jointly adapting the frame rate, spatial resolution and quantization stepsize. In contrast to the conventional approach, the frame rate and spatial resolution are chosen automatically during the coding process and can adapt to a nonstationary source.We introduce a fundamental framework to formalize the description of the M-D bufferconstrained allocation problem. Given a set of operating points on a M-D grid to code a nonstationary source in a buffer-constrained environment, we formulate the optimal solution. The formulation allows a skipped frame to be reconstructed from one coded frame using any temporal interpolation method and is shown to be a generalization of formulations considered in the literature. In the case of intraframe coding, a dynamic programming algorithm is introduced to find the optimal solution. The algorithm allows one to compare operational rate-distortion (R-D) bounds of the M-D and conventional approaches. We also discuss how a solution can be obtained for the case of interframe coding using the optimal dynamic programming algorithm for intraframe coding by making an independent allocation approximation.We experiment with zero-order hold and global motion-compensated temporal interpolation and illustrate that the M-D approach can provide bit rate reductions over 50%. We also show that the M-D approach with limited lookahead provides a slightly suboptimal solution that consistently outperforms the conventional approach with full lookahead. While our algorithm is computationally expensive, it can be directly used for nonreal-time encoding, for benchmarking, and as an aid in the development of suboptimal algorithms.