Loss concealment using B-pictures motion information

In this paper, the motion parameters of the bidirectionally predicted pictures (B-pictures) of MPEG-1,2 are exploited for concealment of large portions of corrupted anchor pictures (and vice versa) that might arise due to channel errors or packet losses. To further enhance the quality of the concealed pictures, we propose two methods of constraining the motion vectors of the B-pictures that strengthen the tie between them and those of the anchor pictures in the same picture subgroup. In one method, the macroblock decisions on the last B-picture in each subgroup is constrained to be bidirectional if those of the other B-pictures are not, such that the derived motion vectors for the concealment of the anchor picture are always composed from the forward and backward motion vectors of the bidirectional motions. Second, the bidirectional motion vectors of the B-pictures in each subgroup is constrained such that the vectorial sum of their forward and backward motion vectors results in an accurate motion prediction of the anchor picture. The experimental results show that while the composed motion vectors improve the quality of concealment over the conventional methods by more than 3-4 dB, another 2 dB improvement can be achieved by constraining the generation of the bidirectional motion vectors.