H.264/MPEG-4 AVC video coding achieves high coding performance by complex inter and intra prediction algorithms. Many fast intra prediction algorithms are proposed to reduce the calculated modes by using hierarchical directional selection or spatial and temporal correlations. If all-zero blocks can be detected before DCT and quantization, the DCT and quantization can be skipped for these blocks. The computation complexity can be reduced further. Early detection algorithms of all-zero blocks for H.264 video coding have been developed in inter motion search. However, these methods cannot be used in intra prediction directly. In this paper, a novel all-zero block detection algorithm for H.264 intra prediction is proposed. In intra 4x4 modes, the SAD calculation is the same as that in inter motion search, but it is much complex in intra 16x16 modes. The Hadamard transform is used for SAD calculation of 16 AC-coefficient blocks, and an extra Hadamard transform is applied for DC block derived from them. The DC and AC thresholds are derived separately according to SAD calculations. The simulation results of all I-frame coding show that the proposed method can save up to 40% computation time in intra prediction with nearly no PSNR loss and less bitrate gain. Furthermore, it is less performance loss in the condition of I-frame and P-frame coding with the same time saving of intra prediction. Our proposed algorithm has no conflict with other fast intra prediction algorithms and can be applied on any other fast intra prediction method to achieve extra computational saving.
This paper proposes a novel fast intra prediction method to optimize H.264/MPEG-4 AVC video coding. In H.264, coding performance is enhanced through spatial prediction besides temporal prediction. In its luminance intra prediction, 4 modes for 16×16 block-size and 9 directional modes for 4×4 block-size are utilized, and the optimal intra mode is selected by R-D optimization, so the intra mode selection results in high coding complexity. To reduce the complexity of intra prediction, the fast hierarchical mode selection method is proposed with fewer modes to be examined, and intermediate computing results are reused. Therefore the intra prediction mode decision process is accelerated greatly. With the proposed fast intra prediction mode selection method, the intra prediction time can be reduced above 30% with less than 2% increase of bitrate, and up to 0.04dB loss in performance compared to the brute intra prediction mode selection method in H.264 reference software. The results are obtained by encoding with all I-frames, and even less performance loss can be achieved with the same time saving if encoding in I, P and B frames. So the complexity of computation can reduce constantly.