In recent years, a number of sophisticated architectures have been proposed to provide VoD service using multicast transmissions. Compared to their unicast counterparts, these multicast VoD systems are highly scalable and can potentially serve millions of concurrent users. Nevertheless, these systems are designed for streaming constant-bit-rate (CBR) encoded videos and thus cannot benefit from the improved visual quality obtainable from variable-bit-rate (CBR) encoding techniques. To tackle this challenge, this paper presents a novel Slice-and-Patch (S&P) algorithm to support VBR video streaming in a multicast VoD system. Extensive trace-driven simulations are conducted to compare performance of the S&P algorithm with two other algorithms based on priority scheduling. Results show that the S&P algorithm outperforms the other two priority scheduling algorithms for most videos. Compared to the CBR counterpart serving videos of the same average bitrate, the S&P algorithm is able to support VBR video streaming with only 50% increase in latency. Given that VBR-encoded video can achieve visual quality comparable to CBR-encoded video at half the bitrate, this S&P algorithm can potentially achieve perform comparable to CBR-based systems when combined with VBR encoding techniques.
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