Variable block size motion compensation has been adopted by the emerging video coding standard H.264. It can represent the motion characteristic in a macroblock more accurately, and therefore reduce the prediction error to achieve high compression gains. On the other hand, it causes high computational complexity in motion estimation at the encoder. The motion estimation exhaustively performed over all modes to find the best mode for inter coding is slow and computationally involved. In order to reduce the complexity, we proposed a fast inter mode decision algorithm for H.264 encoder. The proposed method efficiently determines a suitable block mode according to the motion field distribution and correlation within a macroblock. The experimental results show that the proposed method reduces a considerable amount of complexity at encoder, while the R-D performance of the proposed method is comparable to that of full mode search.
In this paper we proposed a temporal error concealment scheme utilizing the overlapping approach for the block-based video coder. In the proposed algorithm, each pixel of the lost block is recovered by overlapping from four nearest available neighboring blocks. The weighting coefficients used for overlapping have been carefully designed to address the suitable weights on different pixel locations inside the lost block. The weighted extended boundary match is proposed to replace the popularly used boundary match for recovering the lost motion vectors, such that the recovered motion vector can provide the best lost pixel prediction for the overlapping error concealment process. The experimental results were shown by integrating our algorithm into the H.263+ coder.
A fast block-based motion frame interpolation (FMCI) and an adaptive frame skipping scheme (AFS) are proposed for the H.263/H.263+ decoder and encoder, respectively, in this research. The proposed FMCI decoder can successfully interpolate non-coded frames so that a video clip with skipped frames can be played without jerkiness. In the FMCI decoder, the block-based motion fields from the encoder are directly utilized to generate interpolated frames without performing further motion search. Thus, the computational complexity of the interpolation operation is significantly saved. With AFS, the encoder can adaptively choose the frame skip number based on the prediction result of the embedded FMCI. AFS generates a bit stream with a variable frame rate, which can increase the coding efficiency and enhance the performance of the FMCI interpolation at the decoder. FMCI works with any bit stream generated by the standard H.263/H.263+ encoder with or without incorporating AFS.
Fast motion-compensated frame interpolation (FMCI) schemes for the decoder of the block-based video codec operating in low bit rates are examined in this paper. The main objective is to improve the video quality by increasing the frame rate without a substantial increase in the computational complexity. Two FMCI schemes are proposed depending on the motion vector mapping strategy, i.e. the non-deformable and the deformable block-based FMCI schemes. They provide a trade-off of the computational complexity and the visual performance. With proposed schemes, the decoder can perform frame interpolation using motion information received from the encoder. The complexity of FMCI is reduced since no additional motion search in the decoder is needed as required by standard MCI. It has been observed from experimental results that the visual quality of coded low- bit-rate video is significantly improved at the expense of a small increase in decoder's complexity.
An adaptive overlapped block motion compensation (OBMC) scheme, which takes the rate, distortion and complexity factors into account, is proposed in this research. With this scheme, the encoder uses the classification information to determine which blocks could be distorted after OBMC. Then, the BMC search rather than the OBMC search is applied to these blocks. Depending on the allowed computational complexity of the decoder, the encoder chooses the best set of OBMC macroblocks which requires a higher complexity. Other macroblocks simply adopt BMC. Furthermore, the motion bit rat can be reduced by soothing the motion field of BMC blocks during motion search in the encoder. An effective group OBMC motion search scheme is applied to this new adaptive OBMC motion scheme. Experimental results show that the complexity of both the encoder and the decoder is reduced while the visual quality remains the same due to ten improvement in the oversmooth region.
A novel idea to reduce OBMC search complexity based on checkerboard block grouping is proposed in this work. We call the proposed new scheme GOBMC. No iteration is required in the proposed scheme for encoding, since the obtained OBMC motion vector set nearly reaches a local optimal solution in one iteration step and, therefore, the complexity is significantly reduced. The distortion measures, both in terms of PSNR and visual quality, remain about the same as those obtained from iterative OBMC motion search. In decoding, we propose an OBMC reconstruction which reduces the complexity of multiplication by a factor of 38 percent while preserving the visual quality as obtained from BMC search with OBMC reconstruction.