| H.264 video coding standard is announced formally by ITU-U/ISO in March 2003. With the same quality of video, comparing with H.263 and MPEG-4, H.264's bit rate can be reduced to half of the original. The standard is designed to give some new technical solutions to support a broad range of applications, so it attracts much attention in correlative industrial fields. As a kernel process of a video communication system, the rate control algorithm mainly used to control the output quality and content complexity. Video coding is intended to minimize the distortion subject to a constraint bit rate.This paper gives a brief introduction about the present situation of the rate control technology and focuses on analyzing and comparing the rate control technology of H.264/AVC, as well as some improved traditional algorithms appeared in recent years. Against the disadvantages of the traditional algorithms, which will skip upcoming frame(s) as long as the occupation of buffer comes up to some threshold; this paper presents a new Frame-Skipping scheme. The new algorithm, taking both the buffer situation and the frame complexity into consideration, allows some less important frames to be skipped even the buffer is not full, thus there could be enough space for these violently moving frames to be encoded. Experiments show that this algorithm can somewhat improve the quality of those parts with high complexity. We also compare the bits produced by each mode with the average target bits of each macroblock (MB) in a frame to further modify Lagrange multiplier .The objective of these measures is to produce bits as close to the frame target bits as possible. In order to obtain an accurate QP for a frame, we employ a complexity based bit allocation scheme and a QP adjustment method .Simulation results show that the H.264 encoder, using the proposed algorithm, obtains a much smaller deviation and controls the bit rate better. Particularly, it achieves a quite nice visual quality and the buffer is steadier. |
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