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CS 414 – Multimedia Systems Design Lecture 32 – Media Server (Part 1)

CS 414 – Multimedia Systems Design Lecture 32 – Media Server (Part 1). Klara Nahrstedt Spring 2014. Administrative. MP2 demonstrations – Monday, April 14, 5-7pm. Covered Aspects of Multimedia. Audio/Video Presentation Playback. Image/Video Capture. Audio/Video Perception/ Playback.

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CS 414 – Multimedia Systems Design Lecture 32 – Media Server (Part 1)

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  1. CS 414 – Multimedia Systems DesignLecture 32 – Media Server (Part 1) Klara Nahrstedt Spring 2014 CS 414 - Spring 2014

  2. Administrative MP2 demonstrations – Monday, April 14, 5-7pm CS 414 - Spring 2014

  3. Covered Aspects of Multimedia Audio/Video Presentation Playback Image/Video Capture Audio/Video Perception/ Playback Image/Video Information Representation Transmission Transmission Compression Processing Audio Capture Media Server Storage Audio Information Representation A/V Playback CS 414 - Spring 2014

  4. Outline Media Server Requirements Media Server Layered Architecture CS 414 - Spring 2014

  5. Client/Server Video-on-Demand System CS 414 - Spring 2014

  6. Video-on-Demand Systems must be designed with goals: Avoid starvation Minimize buffer space requirement Minimize initiation latency (video startup time) Optimize cost CS 414 - Spring 2014

  7. Media Server Requirements • Real-time storage and retrieval • Media quanta must be presented using the same timing sequence with which they were captured • High-Data Transfer Rate and Large Storage Space • HDTV quality: 1280x720 pixels/frame; 24 bits/pixel -> 81 Mbytes per second • NTCS quality: 640x480 pixels/frame; 24 bits/pixel ->27MBytes per seconds CS 414 - Spring 2014

  8. YouTube Video Server • http://tech.fortune.cnn.com/2010/05/17/youtube-at-5-years-old-2-billion-served-per-day/ • May 2010, 2 Billion videos served per day • More than 24 hours of video uploaded every minute • Videos usually less than 10 minutes long CS 414 - Spring 2014

  9. YouTube Video Server (2011) Source: http://www.youtube.com/t/press_statistics Over 4 B videos are viewed a day 60 hours of video are uploaded every minute Over 800 million unique users visit YouTube each month 70% of YouTube traffic comes from outside US In 2011, YouTube had more than 1 trillion views (140 views for every person on Earth) CS 414 - Spring 2014

  10. YouTube 2014 Source: http://www.youtube.com/t/press_statistics More than 1 billion unique users visit YouTube every month Total number of YouTube videos (2014) – 120 Billion Number of videos uploaded per day – about 200,000 Time required to see all videos – over 600 years Amount of content uploaded every minute – 100 hours 80% of YouTube traffic comes from outside of US CS 414 - Spring 2014

  11. Video Playback Issues • Single Stream Playback • Possible approach – buffer the whole stream • Problem:?? • Possible approach – prefetch just short video part • Problem: • Prevent starvation • Minimize buffer space requirement • Minimize initiation latency • Multiple Streams Playback • Possible approach – dedicate a disk to each stream • Problem: ?? • Possible approach – multiple streams per disk • Problems: ?? CS 414 - Spring 2014

  12. Media Server Architecture Delivered data Incoming request Network Attachment Content Directory/Distribution Memory Management File System Storage management Disk control - scheduling Storage device CS 414 - Spring 2014

  13. Storage Device- Disk Layout Zoned Disk (ZBR – Zone Bit Recording) Traditional Random Access Disk Layout Track Sector Advantage: Sector size same Rotation speed constant; efficient Usage of space Advantage: Easy mapping of location Information to head movement and disk rotation Problem: loss of storage space CS 414 - Spring 2014

  14. Storage/Disk Management • Optimal placement of MM data blocks • Single disk • multiple disks • Timely disk scheduling algorithms and sufficient buffers to avoid jitter • Possible Admission control CS 414 - Spring 2014

  15. Storage Management • Storage access time to read/write disk block is determined by 3 components • Seek Time • Time required for the movement of read/write head • Rotational Time (Latency Time) • Time during which transfer cannot proceed until the right block or sector rotates under read/write head • Data Transfer Time • Time needed for data to copy from disk into main memory CS 414 - Spring 2014

  16. Impact of Access Time Metrics • If data blocks are arbitrarily placed • If requests are served on FCFC basis • Then effort for locating data place may cost time period in order of magnitude 10ms • This performance degrades disk efficiency • Need techniques to reduce seek, rotation and transmission times !!! CS 414 - Spring 2014

  17. MM Data Placement on Single Disk CS 414 - Spring 2014

  18. Intra-file Seek Time • Intra-file seek – can be avoided in non-contiguous layout if the amount read from a stream always evenly divides block • Solution: select sufficient large block and read one block in each round • If more than one block is required to prevent starvation prior to next read, deal with intra-file seek • Solution: constrained placement or log-structure placement CS 414 - Spring 2014

  19. Non-continuous Placement CS 414 - Spring 2014

  20. Constrained Placement • Approach: separation between successive file blocks is bounded • Bound on separation – not enforced for each pair of successive blocks, but only on average over finite sequence of blocks • Attractive for small block sizes • Implementation – expensive • For constrained latency to yield full benefit, scheduling algorithm must retrieve immediately all blocks for a given stream before switching to another stream CS 414 - Spring 2014

  21. Log-Structure Placement • This approach writes modified blocks sequentially in a large contiguous space, instead of requiring seek for each block in stream when writing (recording) • Reduction of disk seeks • Large performance improvements during recording, editing video and audio • Problem: bad performance during playback • Implementation: complex CS 414 - Spring 2014

  22. MM Data Placement at Multiple Disks Data Interleaving On single disk (consecutive blocks are placed on The same cylinder But in interleaved way Data Interleaving On Multiple Disks (Disks are not Synchronized) Striping data across Multiple disks CS 414 - Spring 2014

  23. Disk Scheduling Policies • Goal of Scheduling in Traditional Disk Management • Reduce cost of seek time • Achieve high throughput • Provide fair disk access • Goal of Scheduling in Multimedia Disk Management • Meet deadline of all time-critical tasks • Keep necessary buffer requirements low • Serve many streams concurrently • Find balance between time constraints and efficiency CS 414 - Spring 2014

  24. Disk Scheduling Framework Source: Reddy et al, “Disk Scheduling in a Multimedia I/O System”, ACM TOMCCAP 2005 Must support multiple QoS levels and requests CS 414 - Spring 2014

  25. EDF (Earliest Deadline First) Disk Scheduling • Each disk block request is tagged with deadline • Very good scheduling policy for periodic requests • Policy: • Schedule disk block request with earliest deadline • Excessive seek time – high overhead • Pure EDF must be adapted or combined with file system strategies CS 414 - Spring 2014

  26. EDF Example Note: Consider that block number Implicitly encapsulates the disk track number CS 414 - Spring 2014

  27. Conclusion • Media Server Architecture • Storage Management • Data/file placement on single disk • Data/file placement on multiple disks • Disk Scheduling – important component in the timely delivery of streams • Admission should be done if one cares not to over subscribe CS 414 - Spring 2014

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