With the proliferation of digital video and the popularity of video streaming applications, it is highly desirable to find and access video segments of interest by searching through the content of video at a speed that is faster than a normal playback. The key functions that enable quick browsing of video are fast-forward and fast-reverse playbacks. However, motion-compensated prediction adopted in the current video coding standards drastically complicates these operations. One approach to implement the fast-forward/reverse playback is to store an additional reverse-encoded bitstream in the server. Once the client requests a fast-forward/reverse operation, the server can select an appropriate frame for the client from either the forward-encoded bitstream or the reverse-encoded bitstream by considering the cost of network bandwidth and decoder complexity. Unfortunately, these two bitstreams are encoded separately. The frame in one bitstream may not be exactly identical to the frame in another bitstream. If one of these frames is then used as the reference for the requested frame, which is in another bitstream, it induces mismatch errors. In this paper, a novel H.264 dual-bitstream system aiming at providing the fast-forward/reverse playback based on SP/SI-frames is proposed. The proposed system can completely eliminate mismatch errors when the frame in the reverse-encoded bitstream replaces the frame in the forward-encoded bitstream and vice versa. Experimental results confirm that the proposed system is effective in eliminating mismatch errors so as to enhance the performance of the dual-bitstream system.
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