Adaptive quantization parameter determination for key frames

Based on the rate control scheme in JVT-AA029 for the video encoders using hierarchical B frames, a quantization parameter (QP) determination method is proposed to adaptively determine the QP for key frames. This method firstly utilizes an empirical equation expressing the relation among the starting QP, the available channel bandwidth and the source characteristics to calculate the starting QP for the first key frame of the video sequence. For the other key frames, the target bit budgets and reference QPs are determined based on the actual coding properties of the previous frames. Then the QPs are calculated by employing a rate-distortion model and further adjusted according to the reference QPs. Experimental results show that the proposed method leads to an average improvement of 0.14dB over the performance of the original rate control scheme in JVT-AA029, and by integrating the proposed method, the rate control scheme outperforms the existing state-of-the-art one by 0.77dB on average.