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Efficient Support for Interactive Video Browsing in Clustered CBR Servers

This paper discusses innovative methods for enhancing interactive video browsing operations in clustered Constant Bit Rate (CBR) video servers. It covers various server architectures, including prefetching and grouping approaches, and evaluates their impact on video delivery efficiency. Key topics include fast-forward operations, network bandwidth optimization, and dynamic block scheduling algorithms. Simulation results demonstrate improvements in playback delay and overall user experience. The findings suggest effective strategies for distributing video blocks and managing requests in high-demand scenarios.

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Efficient Support for Interactive Video Browsing in Clustered CBR Servers

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  1. Efficient Support for Interactive Browsing Operations in Clustered CBR Video Servers IEEE Transactions on Multimedia, Vol. 4, No.1, March 2002 Min-You Wu and Wei Shu

  2. Outline • Introduction • Video server architectures • The prefetching approach • The grouping approach • Simulation results

  3. Implementing fast-forward • Increasing network bandwidth • Displaying frames at a higher rate • Without increasing network bandwidth • Reserve a separate encoded video file for each ratio • Block-skipping • Frame-skipping

  4. A clustered video server Delivery node

  5. Server architecture • Storage node • Storing video data • Dealing its own disk scheduling algorithm • Delivery node • Receiving requests from clients • Buffering and resequencing video blocks from storage nodes • Sending video blocks to clients

  6. Distribution of video blocks • A video file is partitioned into many video blocks (CBR) • Video blocks are evenly distributed over N storage nodes in a round-robin fashion. • Block i is stored in the disk (i mod N)

  7. Scheduling of video blocks for normal play Time cycle: time to play a block Time slot: storage node can service multiple requests in a time cycle

  8. The prefetching approach • Block-skipping • When performing an fast-forward operation of ratio f, a block is retrieved after skipping f-1 blocks. • To avoid a hot spot, the number of storage nodes (N) and fast-forward ratio (f) must be relatively prime. • Otherwise, a video file can be distributed to a subset of storage nodes. • For example, if N=4 and f=2, then only storage node 0 and 2 will be accessed.

  9. Layout and access pattern of fast-forward for block-skipping N = 5, F = 3

  10. Prefetching approach for block-skipping retrieve Play

  11. Delay • The delivery node retrieves blocks in the sequence of 0, 6, 12, 3, 9, 15, …and it delivers blocks in the sequence of 0, 3, 6, 9, 12, 15, … • The block 0 needs to be delayed to time t2, so that at time t3 block 3 can be delivered. • Consider an fast-forward operation of ration f starts at tk. The maximum delay

  12. Example of maximum delay for different ratios f

  13. Frame-skipping • Skipping frames within a video block. • Base substream – contains the frames for fast-forward • Enhancement substream – contains the frames only for normal play.

  14. Prefetching approach for frame-skipping

  15. The grouping approach • The pace is defined as the speed of play. • The grouping approach divides requests into different groups based on their paces.

  16. Groups of request with different paces

  17. Operations • Change the membership of a request • Adding • Removing • Change the number of time slots allocated to a group • Expanding • Shrinking

  18. Grouping approach for block-skiiping

  19. Frame-skipping Access f sub-blocks in a time slot

  20. Comparison • Prefetching approach • Fully utilize the system bandwidth • Initial delay • Require some buffer space • Grouping approach • Does not require extra buffer space • The shrinking operation may lead to reallocation and delay of some requests.

  21. Maximum (total) buffer requirement (prefetching approach)

  22. Maximum (total) buffer requirement (prefetching approach)

  23. Average delay and relocation (grouping approach)

  24. Average delay and relocation (grouping approach)

  25. Discuss • Interactive 20% ~ 50% • Pace = 1: 50% ~ 80% (5 ~ 6 time slot) • Pace = 5: 10% ~ 25% (2 time slot) • Pace = 11: 10% ~ 25% (2 time slot) • Expanding and shrinking operations are rarely invoked.

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