One of the most frequently used coding mode in H.264 is skip mode. In the conventional approach, after the best RD
mode has been computed and the resultant predicted error coefficients block is all quantized to zero, it is switched to
skip mode. This is a waste of computational resources because skip mode doesn't require forward transform and
quantization. In this paper, skip mode condition is checked for the macroblock prior to multi-block motion estimation.
Motion estimation will not be performed if the condition is satisfied which will drastically reduce the computations. The
condition considers zero-block property after 4x4 block transform/quantisation and caters for noise inherent in natural
video images. In addition, color components are also taken into consideration for skip mode decision. The experimental
results show that the approach can improve encoder speed greatly with negligible bit rate increase or PSNR degradation.
It is well known that motion estimation is the most computationally intensive processing unit of the H.264 video
encoder. Various fast motion estimation algorithms have been proposed to reduce its complexity. Generally, these
approaches achieve speedup by reducing the number of candidate search points within the search window. In this paper,
we propose a new method, which uses the Sum-of-Absolute-Differences mapping (SAD map) to dynamically cache the
SAD values and then reuse them for different block sizes. Experimental results on standard video sequences verified
that the proposed method is capable of increasing the encoder speed by up to 15% without any loss in PSNR value or
increase in bit rate. Due to its generic nature, this method can be applied in any fast motion estimation methods although
it is especially effective in the full search motion estimation method.
As one important component in H.264 video encoder, interpolation of half and quarter pixels is also computational
intensive. Compared to integer pixel motion estimation, "finer" interpolation provides better block match. However, this
good motion compensation performance is obtained at the expense of increased complexity. Based on our previous
work, this paper presents an improved fast and adaptive interpolation method that further reduces the complexity of
video encoding process. Experimental results on typical video sequences demonstrate that the proposed method is able
to increase encoder speed ranging from 10% to 22% compared with our previous work without any PSNR loss or bit