Jun Xin

Efficient MPEG-2 to H.264/AVC intra transcoding in transform-domain

In this paper, we propose a transform-domain MPEG-2 to H.264/AVC intra video transcoder. In the transcoder, the input DCT coefficients are first converted to H.264 transform (HT) coefficients entirely in the transform-domain. A rate-distortion optimized macroblock mode decision is then performed, based on the HT coefficients. Finally, the HT coefficients are coded using the selected modes to generate the output H.264 bitstream. The proposed transcoder is equivalent to the conventional pixel-domain implementation in terms of functionality, but its complexity is significantly lower (on average over 20%). To further reduce its computational complexity, we propose a fast mode decision algorithm based on a simple cost function calculated in the HT-domain. This fast algorithm reduces the complexity requirement about 50%, while maintaining virtually the same coding efficiency.

An overview of scalable video streaming

During the past two decades, video coding technology has matured and stat-of-the-art coding standards have become very important part of the video industry. Standards such as MPEG2 [16] and H.264/AVC [20] provide strong support for digital video transmission, storage and streaming applications.

Converting DCT coefficients to H.264/AVC transform coefficients

The AVS video coding schemes, which is developed by China, uses a different transform (ICT) than before. The recently completed video coding standard, H.264/AVC, also uses an integer transform, (HT). In this paper, we propose an efficient method to convert ICT coefficients to HT coefficients entirely in the transform domain. We show that the conversion is essentially a 2D transform. We derive the transform kernel matrix and provide a fast algorithm. We show that the proposed transform domain conversion outperforms the conventional pixel domain approach. It is expected to have applications in transform domain video transcoding.

Efficient MPEG-2 to H.264/AVC transcoding of intra-coded video

This paper presents an efficient transform-domain architecture and corresponding mode decision algorithms for transcoding intra-coded video from MPEG-2 to H.264/AVC. Low complexity is achieved in several ways. First, our architecture employs direct conversion of the transform coefficients, which eliminates the need for the inverse discrete cosine transform (DCT) and forward H.264/AVC transform. Then, within this transform-domain architecture, we perform macroblock-based mode decisions based on H.264/AVC transform coefficients, which is possible using a novel method of calculating distortion in the transform domain. The proposed method for distortion calculation could be used to make rate-distortion optimized mode decisions with lower complexity. Compared to the pixel-domain architecture with rate-distortion optimized mode decision, simulation results show that there is a negligible loss in quality incurred by the direct conversion of transform coefficients and the proposed transform-domain mode decision algorithms, while complexity is significantly reduced. To further reduce the complexity, we also propose two fast mode decision algorithms. The first algorithm ranks modes based on a simple cost function in the transform domain, then computes the rate-distortion optimal mode from a reduced set of ranked modes. The second algorithm exploits temporal correlations in the mode decision between temporally adjacent frames. Simulation results show that these algorithms provide additional computational savings over the proposed transform-domain architecture while maintaining virtually the same coding efficiency.

Motion mapping and mode decision for MPEG-2 to H.264/AVC transcoding

This paper describes novel transcoding techniques aimed for low-complexity MPEG-2 to H.264/AVC transcoding. An important application for this type of conversion is efficient storage of broadcast video in consumer devices. The architecture for such a system is presented, which includes novel motion mapping and mode decision algorithms. For the motion mapping, two algorithms are presented. Both efficiently map incoming MPEG-2 motion vectors to outgoing H.264/AVC motion vectors regardless of the block sizes that the motion vectors correspond to. In addition, the algorithm maps motion vectors to different reference pictures, which is useful for picture type conversion and prediction from multiple reference pictures. We also propose an efficient rate-distortion optimised macroblock coding mode decision algorithm, which first evaluates candidate modes based on a simple cost function so that a reduced set of candidate modes is formed, then based on this reduced set, we evaluate the more complex Lagrangian cost calculation to determine the coding mode. Extensive simulation results show that our proposed transcoder incorporating the proposed algorithms achieves very good rate-distortion performance with low complexity. Compared with the cascaded decoder-encoder solution, the coding efficiency is maintained while the complexity is significantly reduced.

Complexity scalable motion estimation for H.264/AVC

A new complexity-scalable framework for motion estimation is proposed to efficiently reduce the motioncomplexity of encoding process, with focus on long term memory motion-compensated prediction of the H.264 video coding standard in this work. The objective is to provide a complexity scalable scheme for the given motion estimation algorithm such that it reduces the encoding complexity to the desired level with insignificant penalty in rate-distortion performance. In principle, the proposed algorithm adaptively allocates available motion-complexity budget to macroblock based on estimated impact towards overall rate-distortion (RD) performance subject to the given encoding time limit. To estimate macroblock-wise tradeoff between RD coding gain (J) and motion-complexity (C), the correlation of J-C curve between current macroblock and collocated macroblock in previous frame is exploited to predict initial motion-complexity budget of current macroblock. The initial budget is adaptively assigned to each blocksize and block-partition successively and motion-complexity budget is updated at the end of every encoding unit for remaining ones. Based on experiment, proposed J-C slope based allocation is better than uniform motion-complexity allocation scheme in terms of RDC tradeoff. It is demonstrated by experimental results that the proposed algorithm can reduce the H.264 motion estimation complexity to the desired level with little degradation in the rate distortion performance.

A Study of MPEG-2 to H.264/AVC Transcoding with Half-Horizontal Resolution

This paper analyzes the performance of MPEG-2 to H.264/AVC transcoding to half-horizontal resolution. Both the quality of the resulting video and complexity of the system are examined in the context of next-generation HDD recording systems. Experimental results show the importance of motion mapping to maintain high picture quality and that quality improvement over full-resolution transcoding is possible. It is also shown that transcoding to half-horizontal resolution allows for substantial reduction in complexity.