Nowadays, video playback devices have only limited fast-forward/backward playback and even they cannot provide backward playback. The limitation is due to the motion compensated prediction technique adopted in the MPEG standards. One possible way to support browsing functionalities is to store an additional reverse-encoded bitstream into the server. However, this additional bitstream increases the storage requirement of the video server significantly. In this paper, we exploit the redundancy inherent between the forward and reverse-encoded bitstreams in order to achieve a substantial reduction on the size of the reverse-encoded bitstream. The server accesses and manipulates various macroblocks from the forward and reverse-encoded bistreams to facilitate various browsing operations. Experimental results show that, as compared to the conventional dual-bitstream scheme, the new scheme significantly reduces the storage requirement due to the additional reverse-encoded bitstream.

MPEG digital video is becoming ubiquitous for video storage and communications. It is often desirable to perform various video cassette recording (VCR) functions such as backward playback in MPEG videos. However, the predictive processing techniques employed in MPEG severely complicate the backward-play operation. A straightforward implementation of backward playback is to transmit and decode the whole group-of-picture (GOP), store all the decoded frames in the decoder buffer, and play the decoded frames in reverse order. This approach requires a significant buffer in the decoder, which depends on the GOP size, to store the decoded frames. This approach could not be possible in a severely constrained memory requirement. Another alternative is to decode the GOP up to the current frame to be displayed, and then go back to decode the GOP again up to the next frame to be displayed. This approach does not need the huge buffer, but requires much higher bandwidth of the network and complexity of the decoder. In this paper, we propose a macroblock-based algorithm for an efficient implementation of the MPEG video streaming system to provide backward playback over a network with the minimal requirements on the network bandwidth and the decoder complexity. The proposed algorithm classifies macroblocks in the requested frame into backward macroblocks (BMBs) and forward/backward macroblocks (FBMBs). Two macroblock-based techniques are used to manipulate different types of macroblocks in the compressed domain and the server then sends the processed macroblocks to the client machine. For BMBs, a VLC-domain technique is adopted to reduce the number of macroblocks that need to be decoded by the decoder and the number of bits that need to be sent over the network in the backward-play operation. We then propose a newly mixed VLC/DCT-domain technique to handle FBMBs in order to further reduce the computational complexity of the decoder. With these compressed-domain techniques, the proposed architecture only manipulates macroblocks either in the VLC domain or the quantized DCT domain resulting in low server complexity. Experimental results show that, as compared to the conventional system, the new streaming system reduces the required network bandwidth and the decoder complexity significantly.

Digital video cassette recording (VCR) operations such as fast-forward and fast-reverse playbacks enable quick and user-friendly browsing of video. However, the predictive techniques adopted in current video standards severely complicate these operations. One approach to implement the fast-forward/reverse playback is to store an additional reverse-encoded bitstream into the server. Once a client requests a fast-forward/reverse operation, the server can select an appropriate frame for the client from either the forward or reverse-encoded bitstreams to reduce the network traffic and the decoder complexity. Unfortunately, the forward and reverse-encoded bitstreams are encoded separately. The frame that has previously decoded by the client may not be exactly identical to the reference of the current selected frame and the mismatch problem occurs frequently. In this paper, a novel H.264 dual-bitstream scheme aiming at providing fast-forward/reverse playback based on SP/SI-frames is proposed to eliminate mismatch errors during switching between the forward and reverse-encoded bitstreams. As a result, the proposed scheme enhances the performance of the conventional dual-bitstream scheme.