Keng Pang Lim

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.

Fast intermode decision in H.264/AVC video coding

The new video coding standard, H.264/MPEG-4 AVC, uses variable block sizes ranging from 4/spl times/4 to 16/spl times/16 in interframe coding. This new feature has achieved significant coding gain compared to coding a macroblock (MB) using fixed block size. However, this feature results in extremely high computational complexity when brute force rate distortion optimization (RDO) algorithm is used. This paper proposes a fast intermode decision algorithm to decide the best mode in intercoding. It makes use of the spatial homogeneity and the temporal stationarity characteristics of video objects. Specifically, spatial homogeneity of a MB is decided based on the MBs edge intensity, and temporal stationarity is decided by the difference of the current MB and it colocated counterpart in the reference frame. Based on the homogeneity and stationarity of the video objects, only a small number of intermodes are selected in the RDO process. The experimental results show that the fast intermode decision algorithm is able to reduce on the average 30% encoding time, with a negligible peak signal-to-noise ratio loss of 0.03 dB or, equivalently, a bit rate increment of 0.6%.

Adaptive rate control for H.264

This paper presents a rate control scheme for H.264 by introducing the concept of basic unit and a linear prediction model. The basic unit can be a macroblock (MB), a slice, or a frame. It can be used to obtain a trade-off between the overall coding efficiency and the bits fluctuation. The linear model is used to solve the chicken and egg dilemma existing in the rate control of H.264. Both constant bit rate (CBR) and variable bit rate (VBR) cases are studied. Our scheme has been adopted by H.264.

A study of MPEG-4 rate control scheme and its improvements

This paper discusses some practical issues in implementing the MPEG-4 Q2 rate-control scheme, and proposes a number of ways to improve it. The improved algorithm has the following main features: (1) the bits allocated to each P-frame or B-frame are in proportion to its distance from the end this GOP. i.e., more bits are allocated to the frames that are nearer to their reference I-frame; (2) the target buffer level is a function of the frame position in the GOP, so that it will be achieved gracefully at the end of a GOP; and (3) the quantization value of an I-frame is decided based on its spatial complexity. Experimental results show that the improved rate-control scheme has significantly reduced the occurrence of frame skipping, increased the average PSNR by up to 0.6 dB, and improved the perceptual quality of the reconstructed video.

A directional field based fast intra mode decision algorithm for H.264 video coding

The H.264 video coding standard can achieve considerably higher coding efficiency than previous standards. In order to achieve this, a robust rate-distortion optimization (RDO) technique is employed to select the best coding mode for each macroblock. As a result. the encoder complexity is increased considerably. This paper presents a directional field based fast intra mode decision algorithm to improve the encoders efficiency. Prior to intra prediction, the directional field is calculated for all the block size to decide the dominant edge direction in the blocks. Based on the edge direction information, only a small number of prediction modes are chosen for RDO calculation. Experimental results show that the fast intra mode decision algorithm increases the speed of intra coding significantly with negligible loss of PSNR

Block INTER mode decision for fast encoding of H.264

The paper presents a fast block INTER mode decision algorithm to improve significantly the time efficiency of the encoder in H.264. It makes use of the spatial homogeneity of a video objects textures and the temporal stationarity characteristics inherent in video sequences. Specifically, the homogeneity decision of a block is based on edge information, and MB differencing is used to judge whether the MB is time-stationary. Based on the above analysis, only parts of inter prediction modes are chosen for RDO (rate distortion optimization) calculation. Experimental results show that the new scheme is able to achieve a reduction of 30% encoding time on average, with a negligible average PSNR loss of only 0.03 dB and a mere 0.6% bit rate increase compared with the original H.264 reference software.

Adaptive intra-frame quantization for very low bit rate video coding

This paper presents, for I-frames, a generic relationship among the quantization value, data bits, and their spatial complexity. This relationship provides a mechanism to select the quantization value for an I-frame (with different spatial complexity) at given bit budget before actually encoding it. Therefore it helps to adaptively distribute the bit budget among I-, P- and B-frames in a sequence. Experiments show that the adaptive intra frame quantization algorithm reduces the number of frame skippings significantly with comparable average PSNRs, and thus improves the overall subjective quality of the reconstructed video.

Video streaming on embedded devices through GPRS network

We introduce a PDA-based live video streaming system on GPRS network based on MPEG-4 video compression standard. Due to the limited computational resources of PDA, all the key modules of MPEG-4 codec are efficiently implemented and optimized such as multithreading, buffer design, wireless communication, encoder and decoder. Several novel techniques are developed in the coding, streaming as well as the post- processing stages of the system.

Adaptive frame layer rate control for H.264

This paper proposes an adaptive frame layer rate control scheme for H.264 by introducing a linear model to predict the mean absolute difference (MAD) of current frame by that of previous one. The target bit rate for each frame is computed by adopting a fluid flow traffic model and linear tracking theory. The corresponding quantization parameter is computed by using a quadratic rate-distortion model. The rate distortion optimization (RDO) is then performed for all macroblocks (MBs) in the current frame by the quantization parameter. Both constant bit rate (CBR) and variable bit rate (VBR) cases are studied. The average PSNR is improved up to 0.75 dB compared to an encoder with fixed quantization parameter.

An Adaptive Thresholding Technique for the Detection of All-Zeros Blocks in H. 264

In H.264 video coding, there are a substantial number of 4x4 blocks becoming all-zeros after transformation and quantization. This is a waste of computational resources because these skipped blocks do not require forward transform and quantization. We proposed a very effective early detection of fast skipped block detections based on the theoretical derivation of H.264 integer transform and quantization. The experimental results show that the algorithm can detect 9.71%-43.35% more zero blocks than Yongs method.