| Along with the development of internet technology and mobile communication technology, demands for video communications, such as video phone, video monitoring, and video conference have been greater and greater. Compared with the previous standards, the newly proposed international standard H.264/AVC and national standard AVS provide better network adaptability and higher compression efficiency, which speed up the application of video technology over network.In order to make sufficient use of such limited and variable bandwidth, the size of bit streams of coded video should be controlled within a certain range. Thus, rate control plays an important role in an encoder, and a good rate control scheme is meant to guarantee the video quality under fluctuate, limited and variable bandwidth.This paper first analyses main factors that influence bit numbers and introduces several classical rate control algorithms. As for the shortcomings in those algorithms, some improvements are proposed in the paper, including two aspects:for that the method of calculatingâ… frame quantization parameter is too simple, a method based on the complexity of frames and remaining bit numbers is proposed; and as the rate control around scene cuts is not considered, a method combiningâ… frame rate control and adaptive GOP length is also discussed in the paper. Results show that our methods provide better performance than the original rate control algorithms in terms of buffer state and PSNR smoothness.This paper also makes some experiments on how frame rate and resolution make influence on video quality. According to the results, we find in low bit rate, lowering the resolution or frame rate of the video before coding it could make better quality of experience. With those findings, a novel scheme of adaptive resolution and frame skip is proposed, and results show ours provide better performance in low bit rate condition, meanwhile, our method is compatible with current standards and has practical application value. |
PDF Full Text Request