Efficient reverse-play algorithms for MPEG video with VCR support

Abstract

Reverse playback is the most common video cassette recording (VCR) function in digital video players and it involves playing video frames in reverse order. However, the predictive processing techniques employed in MPEG severely complicate the reverse-play operation. For displaying single frame during reverse playback, all frames from the previous I-frame to the requested frame must be sent by the server and decoded by the client machine. It requires much higher bandwidth of the network and complexity of the decoder. In this paper, we propose a compressed-domain approach for an efficient implementation of the MPEG video streaming system to provide reverse playback over a network with the minimal requirements on the network bandwidth and the decoder complexity. In the proposed video streaming server, it classifies macroblocks in the requested frame into two categories-backward macroblocks (BMBs) and forward macroblock (FMBs). Two novel MB-based techniques are used to manipulate the necessary MBs in the compressed domain and the server then sends the processed MBs to the client machine. For BMBs, we propose a sign inversion technique, which is operated in the variable length coding (VLC) domain, to reduce the number of MBs that need to be decoded by the decoder and the number of bits that need to be sent over the network in the reverse-play operation. The server also identifies the previous related MBs of FMBs and those related maroblocks coded without motion compensation are then processed by a technique of direction addition of discrete cosine transform (DCT) coefficients to further reduce the computational complexity of the client decoder. With the sign inversion and direct addition of DCT coefficients, the proposed architecture only manipulates MBs either on the VLC domain or DCT domain to achieve the server with low 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.