Fast Mode Decision Research Articles

Efficient rate-distortion estimation for H.264/AVC coders

In video coders, the optimal coding mode decision for each coding block can be achieved by exhaustively calculating the rate-distortion cost, which simultaneously considers the distortion performance and the coding bit consumption of all possible modes. The best mode is chosen from the one with the minimum Lagrange cost. To avoid the expensive computation of Lagrange costs, in this paper, we propose transform-domain bit-rate estimation and distortion measures, based on quantized and inverse quantized integer transform coefficients, for the inter-mode decision in H.264/AVC coders. With the proposed scheme, entropy coding, inverse transform, and pixel-reconstructions are not required in the process. With ignorable degradation in coding performance, simulations demonstrate that the proposed estimation method achieves about 40% reduced computation time of rate-distortion cost for the inter-mode decision and saves about 17% total encoding time while combining with fast motion estimation and fast mode decision algorithms.

Fast motion estimation and mode decision for H.264 reverse transcoding

A fast reverse motion estimation algorithm with smart mode decision for H.264 reverse transcoding is proposed. The best mode for the backward transcoded macroblock is obtained by analysing the motion vectors and modes decoded from the forward bitstream. A significant reduction in the transcoding complexity with negligible impact on rate-distortion performance has been achieved.

Fast mode decision algorithm for spatial resolutions down-scaling transcoding to H.264

A fast mode decision algorithm is proposed in this paper to accelerate the process of transcoding videos into H.264 with arbitrary rate spatial resolution down-scaling. The proposed algorithm consists of three steps. First, an early-stop technique is introduced to determine the 16×16-mode blocks, which take up about 70% of all the macroblocks; then, a bottom-up merging process is performed to determine the mode of rest non-early-stopped blocks; and then, we adopt half-pixel motion estimation to further refine the acquired predictive motion vectors. In order to obtain the predictive motion vectors for early-stop and merging processes, we propose a motion vector composition scheme, which can reuse the information in the input pre-encoded videos to handle the spatial resolution down-scaling. Experimental results showed that our algorithm is about four times faster than the Cascaded-Decoder-Encoder method and has negligible PSNR drop and little bit rate increase.

A framework for fast mode decision in the H264 video coding standard

We propose a novel framework for fast mode decision in the simple and main profiles of the H264 video coding standard. Our framework consists of a specific combination of algorithms, each achieving computational savings while retaining rate distortion (RD) performance very similar to the standard. In particular, we utilise a set of skip mode conditions for P and B slices, two heuristics that reduce the cardinality of the inter mode set to be examined, inter/intra mode prediction and the monotonicity property of the rate distortion cost functions. We achieve content dependent savings in run times between 5.8 and 90.1% as compared to H264. Compared to other work that was used as input to the standard, our scheme is faster by 9-23% for very similar RD performance. The proposed framework can be used wholly or partially for computational speed-ups, it is independent of the motion search method used and is applicable in both the rate controlled and nonrate controlled cases.

Fast motion search with efficient inter-prediction mode decision for H.264

A fast inter-prediction mode decision and motion search algorithm is proposed for the H.264 video coding standard. The multi-resolution motion estimation scheme and an adaptive rate-distortion model are employed with early termination rules to accelerate the search process. With the new algorithm, the amount of computation involved in the motion search can be substantially reduced. Experimental results show that the proposed algorithm can achieve a speed-up factor ranging from 60 to 150 times as compared to the full-search algorithm with little quality degradation.

Fast mode decision algorithm for intraprediction in H.264/AVC video coding

The H.264/AVC video coding standard aims to enable significantly improved compression performance compared to all existing video coding standards. In order to achieve this, a robust rate-distortion optimization (RDO) technique is employed to select the best coding mode and reference frame for each macroblock. As a result, the complexity and computation load increase drastically. This paper presents a fast mode decision algorithm for H.264/AVC intraprediction based on local edge information. Prior to intraprediction, an edge map is created and a local edge direction histogram is then established for each subblock. Based on the distribution of the edge direction histogram, only a small part of intraprediction modes are chosen for RDO calculation. Experimental results show that the fast intraprediction mode decision scheme increases the speed of intracoding significantly with negligible loss of peak signal-to-noise ratio.