In the conventional video codec, B pictures usually employ five prediction modes. including bi-prediction, direct prediction, fonvard prediction, backward prediction and intra modes. Among them. the direct and bi-prediction modes. whose prediction values are ochievedfiom bothforward and backword reference pictures, are more efticient in uploiring the temporal correlation between the reference pictures and the current B picture- In oddition, the direct mode does not require any bits for coding the motion vectors. Therefure, the blocks coded with direct or bi-predictive mode are usually much more than the other modes. To further take advantage of the bi-prediction, in this paper we propose a new bi-predictive coding technique, which can achieve the good tradeofbetween the bit-rate soving for motion vcctor coding and the prediction accwacy. Moreover, we also propose the spotiol motion vector prediction and motion vector scaling techniques to improve the accuracy of derived direct mode morion vectors. All these techniques hove been adopted in A VS' video coding standard,
['Xiangyang Ji', 'Debin Zhao', 'Wen Gao', 'Qingming Huang', 'Siwei Ma', 'Yan Lu']
NEW BI-PREDICTION TECHNIQUES FOR B PICTURES CODING