Dynamic rate shaping of compressed digital video

Abstract

We discuss new theoretical and experimental results on the dynamic rate shaping (DRS) approach for transcoding compressed video bitstreams (MPEG-1, MPEG-2, MPEG-4, H.261, as well as JPEG). We analyze the behavior of DRS assuming a first order autoregressive source. We propose a set of low complexity algorithms for both constrained and unconstrained DRS and substantiate the almost-optimal experimental performance of the memoryless algorithm by assuming a first order autoregressive source. By deriving the statistical and rate-distortion characteristics of different components of the interframe rate shaping problem, we offer an explanation as to why the set of optimal breakpoint values for any frame is somewhat invariant to the accumulated motion compensated shaping error from past frames. We also present an extensive experimental study on the various DRS algorithms (causally optimal, memoryless, and rate-based) both in their constrained and generalized forms. The study proves the computational viability of the DRS approach to transcoding and identifies a range of rate shaping ratios for which it is better than requantization, both complexity-wise as well as in performance. This result is significant in that it opens up the way to construct much simpler memoryless algorithms that give minimal penalty in achieved quality, not just for this but possibly other types of algorithms. This is also the very first use of matrix perturbation theory for tracking the spectral behavior of the autocorrelation matrix of the source signal and the motion residual it yields.

An Optimal Framework of Video Adaptation and Its Application to Rate Adaptation Transcoding

“…We implement our CD using the Lagrange optimization algorithm based on the work in [8] with some modifications. Specifically, instead of using MB-level dropping (that is, each MB has a unique dropping point shared by all four luminance and two chrominance blocks), we use a block-level search to find individual dropping points for each block.…”

“…However, the causally optimal algorithm that ignores the propagation error can be a practical approach to avoid complexity and delay due to "look-ahead" optimization. For further simplification to be deployed at proxies, we finally adopt the memoryless algorithm [8] that ignores the accumulated error and treats each picture as an intra one in the generation of utility function. It was reported that ignoring the accumulated errors does not much affect the quality and allows achieving essentially optimal (with a difference of about 0.2 dB) performance in a typical size of GOP [8].…”

“…For further simplification to be deployed at proxies, we finally adopt the memoryless algorithm [8] that ignores the accumulated error and treats each picture as an intra one in the generation of utility function. It was reported that ignoring the accumulated errors does not much affect the quality and allows achieving essentially optimal (with a difference of about 0.2 dB) performance in a typical size of GOP [8]. A very simple alternative approach that can serve as a lower bound in terms of quality is a purely rate-based approach.…”

“…An alternative to requantization, which is called DCT coefficient dropping (CD) or dynamic rate shaping (DRS), is to directly cut high-frequency coefficients from each macroblock (MB) without requantization-like processing [8]. Frame dropping (FD) is a temporal domain technique to reduce the bit-rate by reducing temporal resolution with frame skipping.…”

An Adaptive Control for the Propagation Errors Incurred by DCT Coefficient-Dropping Transcoder

“…Furthermore, the FD-CD scheme can achieve rate shaping across a wide range of rate reduction while maintaining spatial-temporal quality as much as possible. For a particular FD-CD operation, in which nonreference frames (namely, B frames) are dropped to avoid the decoding dependency, CD is applied to meet the available bandwidth quite accurately by adjusting the number of dropped coefficients.Some previous studies on FD-CD transcoders have focused on the optimal selection of the number of dropped coefficients within a frame [1], [5]- [9]. The dynamic rate shaping (DRS) approach was introduced as a technique to adapt the rate of compressed video bit-streams [10].…”