Test Model 5 Research Articles

Spatiotemporal adaptive quantization for an efficient video rate control

A new algorithm for the rate control of videos considering the sensitivity of the human visual system (HVS) is presented. The method adopts the three-step structure of MPEG-2 Test Model 5 (TM5) rate control, while a new measure for the macroblock (MB) activity based on spatiotemporal sensitivity is introduced. Experimental results show that the proposed activity measure outperforms the spatial activity of TM5 in picture quality.

Implementation of digital HDTV encoder with parallel sub-picture encoding modules and its joint bit-allocation strategy

Parallel processing is a feasible scheme for a digital HDTV encoder, to get round the dilemma in high-speed digital processing circuitry and real-time compression. This paper suggests an implementation procedure and a novel bit-allocation strategy for a digital high definition television (HDTV) encoder system with parallel processing architecture based on six horizontal strips division. Multiple sub-pictures encoding modules (SEMs) perform MPEG-2 coding respectively and simultaneously. Owing to the inherent deficiencies of MPEG-2 Test Model 5 (TM5) rate control scheme, how to allocate bit-rate among sub-pictures would become an inevitable challenge, which might behave with the coding quality to decrease worse and the buffer to underflow at scene changes, moreover give birth to non-consistent sub-pictures visual quality and dynamic quality variation in a composite HDTV frame on subjective and objective evaluation. We adapt a hierarchical joint optimized bit-allocation with sub-pictures' average complexity measure and average bits per pixel in terms of their average quantization distortion, moreover incorporates scene detection to alleviate a possible worse sub-pictures quality inconsistency. In the paper, we describe an elaborate procedure including general framework, sub-pictures division module, sub-picture encoding module and sub-pictures synthesis module, then deduce the joint bit-allocation strategy for sub-pictures encoding and the auxiliary rate adaptive procedure for scene changes. Experimental results demonstrate that our proposed scheme not only alleviates the boundary effect, but also promises the sub-pictures quality consistency. The proposed scheme might be devoted to the multiprogram broadcast application and the multiple access sceneries.

Rate control of MPEG video for consistent picture quality

We propose a rate control scheme using a rate-distortion (R-D) estimation model, which produces a consistent picture quality between consecutive frames. Our R-D estimation method offers a closed-form mathematical model that enables us to predict the bits and the distortion generated from a frame encoded at a given quantization parameter (QP) and vice versa. Its most attractive feature is its low computational complexity. Furthermore, it is accurate enough to be applied to practical video coding. In our simulation, the estimation errors for rate and distortion are less than 2.5% and 1.5%, respectively. Therefore, the proposed rate control scheme is appropriate for applications requiring low delay, low complexity, and the ability to control output bit-rate and quality accurately. Our scheme ensures that the video buffers do not underflow or overflow by satisfying the buffer constraint, and it also prevents quality difference between consecutive frames from exceeding a certain demanded level by adopting a distortion constraint. In addition, a consistent picture quality is maintained within a frame, and error propagation, caused by quality degradation of anchor frames, is reduced by differentiating the control procedure for anchor frames from that for nonanchor frames. Simulation results show that our control scheme achieves 0.52-1.84 dB peak signal-to-noise ratio (PSNR) gain over MPEG-2 Test Model 5 (TM5) rate control and maintains very consistent quality within a frame as well as between frames.

Rate control for MPEG video coding

ISO/IEC MPEG-2 Test Model 5 (TM5) describes a rate control method which consists of three steps: bit allocation, rate control and modulation (ISO/MPEG II, Test Model 5, April 1993). There are, however, two problems associated with TM5 rate control: degradation in picture quality at scene cuts and nonuniform picture quality due to buffer-dependent variations of the quantization parameter. This paper presents a new rate control approach which addresses these issues. To eliminate the impact of scene cuts on the picture quality, the first scheduled P picture in a new scene is coded as an I picture, and the extra I picture is further balanced by coding the next scheduled I picture as a P picture. To achieve a relatively uniform picture quality, the same global quantization parameter is applied to all the macroblocks in a picture. The global quantization parameter is determined by using either an iterative or a binary search algorithm. The simulation results demonstrate that a significant improvement in performance is obtained using the proposed rate control approach.

Bit-rate control using piecewise approximated rate-distortion characteristics

Digital video's increased popularity has been driven to a large extent by a flurry of international standards (MPEG-1, MPEG-2, H.263, etc). In most standards, the rate control scheme, which plays an important role in improving and stabilizing the decoding and playback quality, is not defined, and thus different strategies can be implemented in each encoder design. Several rate-distortion (R-D)-based techniques have been proposed aimed at the best possible quality for a given channel rate and buffer size. These approaches are complex because they require the R-D characteristics of the input data to be measured before making quantization assignment decisions. We show how the complexity of computing the R-D data can be reduced without significantly reducing the performance of the optimization procedure. We propose two methods which provide successive reductions in complexity by: (1) using models to interpolate the rate and distortion characteristics, and (2) using past frames instead of current ones to determine the models. Our first method is applicable to situations (e.g., broadcast video) where a long encoding delay is possible, while our second approach is more useful for computation-constrained interactive video applications. The first method can also be used to benchmark other approaches. Both methods can achieve over 1 dB peak signal-to-noise rate (PSNR) gain over simple methods like the MPEG Test Model 5 (TM5) rate control, with even greater gains during scene change transitions. In addition, both methods make few a priori assumptions and provide robustness in their performance over a range of video sources and encoding rates. In terms of complexity, our first algorithm roughly doubles the encoding time as compared to simpler techniques (such as TM5). However, the complexity is greatly reduced as compared to methods which exactly measure the R-D data. Our second algorithm has a complexity marginally higher than TM5 and a PSNR performance slightly lower than that of the first approach.

A frequency-domain video transcoder for dynamic bit-rate reduction of MPEG-2 bit streams

Many of the forthcoming video services and multimedia applications are expected to use preencoded video for storage and transmission. Video transcoding is intended to provide transmission flexibility to preencoded bit streams by dynamically adjusting the bit rate of these bit streams according to new bandwidth constraints that were unknown at the time of encoding. In this paper, we propose a drift-free MPEG-2 video transcoder, working entirely in the frequency domain. The various modes of motion compensation (MC) defined in MPEG-2 are implemented in the discrete cosine transform (DCT) domain at reduced computational complexity. By using approximate matrices to compute the MC-DCT blocks, we show that computational complexity can be reduced by 81% compared with the pixel domain approach. Moreover, by using a Lagrangian rate-distortion optimization for bit reallocation, we show that optimal transcoding of high-quality bit streams can produce better picture quality than that obtained by directly encoding the uncompressed video at the same bit rates using a nonoptimized Test Model 5 (TM5) encoder.

IDCT output range before clipping in MPEG video coding

Abstract The precision of the IDCT output before clipping in an MPEG hardware decoder should be sufficient to cover the maximum output range of the IDCT transform. This paper has theoretically proved that the IDCT output range is [−1805, 1805], and in order to avoid IDCT overflow, at least 11 bit or maximal 12 bit should be used to represent the IDCT output of MPEG video coding with TM5 (Test Model 5, Draft version 2) quantizer before its clipping.

A new algorithm on MPEG-2 target bit-number allocation at scene changes

The bit-number allocation strategy of Test Model 5 (TM5) may cause the coding quality to decrease and the buffer to overflow at scene changes, therefore a new algorithm on MPEG-2 target bit-number allocation is proposed in this letter. Here the influence of scene changes on coding quality is analyzed and an approach to improve the coding performance at scene changes is presented to avoid a sharp quality decrease of scene-change frames. Simulation results indicate that this algorithm provides a promising coding quality at scene changes.

Radial basis function video rate estimator for constantbit rate MPEG coders

The authors apply a radial basis function (RBF) network to constant bit rate control for an MPEG2 video encoder. The non-stationary property of the video data has been exploited effectively by using the RBF network as a rate estimator in a feedforward rate control algorithm. The performance of this scheme is evaluated in comparison with Test Model 5 (TM5), by measuring video rate and picture quality.