Abstract: In wireless video transmission system, the network bandwidth is often limited and changing, which leads to poor quality and instability of the video information in this process. Therefore, a rate control regulation was needed in the video codec. In order to make up for the deficiency of Average Bit-Rate (ABR) algorithm in X264, two methods were proposed in this article. According to the gap between actual output bits and target ones, one is a new compensation algorithm in the frame layer to adjust the Quantization Parameters (QP) of the current frame and the other is to rewrite the growth function of the buffer to control its excessive growth. These two methods have been evaluated with different target bits but the same video sequence, and with different video sequences but the same target bits, respectively. The results show that actual output bit rate is closer to the target one on condition that the average Peak Signal-to-Noise Ratio (PSNR) stays the same.

Key words: X264, video coding, rate control, Average Bit-Rate (ABR), Quantization Parameter (QP)

摘要： 无线视频传输系统中,网络带宽往往是有限和动态变化的,这将导致视频信息在传输过程中的质量差以及不稳定,此时需要在视频编解码中采用码率控制进行调控。针对X264平均比特率(ABR)算法的不足,提出了两种改进措施:其一,根据实际输出比特和目标比特之差在帧层增加补偿算法来调整当前帧的量化参数(QP); 其二,改善缓存区增长函数以限制缓存区的过快增长。改进算法通过对同一视频序列不同目标码率以及不同视频序列同一目标码率两种方式进行实验仿真验证。仿真结果表明,在峰值信噪比(PSNR)平均值基本不变的情况下,输出的实际码率更加接近于目标码率。

关键词: X264, 视频编码, 码率控制, 平均比特率, 量化参数