To realize frame rate transcoding, the forward frame repeat mechanism is usually adopted to compensate the skipped frames in the video decoder for end-user. However, based on our observation, it is unsuitable for repeating all skipped frames only in the forward direction and sometimes the backward repeat may achieve better results. To deal with this issue, we propose the new reference frame selection method to determine the direction of repeat-frame for skipped Predictive (P) and Bidirectional (B) frames. For P-frame, the non-zero transformed coefficients and the magnitude of motion vectors are taken into consideration to determine the use of forward or backward repeat. For B-frame, the magnitude of motion vector and its corresponding reference directions of the blocks in B-frame are selected to be the decision criteria. Experimental results show that the proposed method provides 1.34 dB and 1.31 dB PSNR improvements in average for P and B frames, respectively, compared with forward frame repeat.
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