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					 CS 414 – Multimedia Systems Design
 Lecture 28 –
 Media Server (Part 4)

Klara Nahrstedt
Spring 2011

     CS 414 - Spring 2011
    Administrative
   MP3 has
      Two options of MP3
         Option 1 – 2-way video chat: Linux – Android (eligible for competition)

         Option 2 – 3-way video conference: Linux-Linux

         You should decide on one option (either option 1 or option 2)!!!

      April 29, 5-7pm, Google Competition for Option 1 solutions
         Competition with judges via demos in SC 216

         Finalists will demonstration to judges between 5-7pm, April 29

         Finalists will prepare 5 minutes power point presentation

      April 27, 7-9pm, Preview of the MP3 status
         Wednesday, April 27, 7-9pm via demos in SC 216 in front of Prof.
          Nahrstedt and TA Shu
         All groups show their status

         Decision on which groups with option 1 will go towards Google competition



                                   CS 414 - Spring 2011
Administrative
   MP3 has
       April 29, Demonstration of projects (except of finalists)
          Demos for grade between 2-4:30pm in SC 216 to Prof. Nahrstedt
           and TA Shu Shi
       Sign-up sheet for demonstrations
          Provided in class during week of April 22.

       April 29, midnight, code submission via compass
          More details about competition, and others will be posted one week
           prior to competition




                                CS 414 - Spring 2011
Some Facts
 Flickr – image and video hosting website
 In September 2010,
     Fickrhosted more than 5 billion images
     Developed by Ludicorp, Vancouver, 2004, now
      owned by Yahoo!
   In August 2009,
     Flickr   hosted 62 databases across 124 servers


                        CS 414 - Spring 2011
Outline
   Multimedia File System
     Fileallocation tables/Index tables
     Additional File System Operations
     Block sizes

   Efficient Video-on-Demand Service
    Techniques
     Caching
     Patching
     Batching        CS 414 - Spring 2011
Multimedia File Systems
   Real-time Characteristics
     Read  operation must be executed before well-defined
      deadline with small jitter
          Additional buffers smooth data
   File Size
     Can  be very large even those compressed
     Files larger than 2 32 bytes

   Multiple Correlated Data Streams
     Retrievalof a movie requires processing and synch of
      audio and video streams

                              CS 414 - Spring 2011
Placement of Mapping Tables
 Fundamental Issue: keep track of which
  disk blocks belong to each file (I-nodes in
  UNIX)
 For continuous files/contiguous placement
     don’t need    maps
   For scattered files
     Need   maps
        Linked lists (inefficient for multimedia files)
        File allocation tables (FAT)

                          CS 414 - Spring 2011
Indexing and FAT
 Higher Level
 Index Table      File Allocation Table
 Per File
                 Block I1 Location PTR
  I Frame
                 Block I2 Location PTR
  P Frame
                 Block I3 Location PTR
  B Frame
                 Block P11 Location PTR
  P Frame
                 Block P12 Location PTR
 ………..
                 Block B1 Location PTR
                 Block P21 Location PTR
                 Block P22 Location PTR
                 …………..

                CS 414 - Spring 2011
Constant and Real-time Retrieval of
MM Data
   Retrieve index in real-time
   Retrieve block information from FAT
   Retrieve data from disk in real-time
   Real-time playback
       Implement linked list

   Random seek (Fast Forward, Rewind)
     Implement      indexing
   MM File Maps
     include   metadata about MM objects: creator of video,
        sync info
                                CS 414 - Spring 2011
Fast Forward and Rewind
(Implementation)
   Play back media at higher rate
       Not practical solution
   Continue playback at normal rate, but skip
    frames
       Define skip steps, e.g. skip every 3rd, or 5th frame
       Be careful about interdependencies within MPEG frames
   Approaches for FF:
       Create a separate and highly compressed file
       Categorize each frame as relevant or irrelevant
       Intelligent arrangement of blocks for FF

                                 CS 414 - Spring 2011
Block Size Issues in File Organization
   Small Block Sizes
       Use smaller block sizes, smaller than average frame size
   Organization Strategy: Constant Time Length
   Need Metadata structure, called Frame Index
     Frame means    a time frame within a movie
     Under the time frame read all blocks (audio, video,                  Movie
      text) belonging to this time frame                                   Time
                                                                           line
                                                                   Frame
                            ………
                                                                   index


     A V      A V V     A

     V T      V T       V
                              CS 414 - Spring 2011
    Block Size Issues
   Large Block Size
         Uselarge blocks (e.g., 256 KB) which include multiple
         audio/video/text frames
   Organization Strategy: Constant Data Length
   Need Metadata structure, called Block Index
         Each   block contains multiple movie frames

                                                           Block
                                                           Index

    A V         A V    A V
    A           V V    V
                               CS 414 - Spring 2011
Tradeoffs
   Frame index : needs large RAM usage while
    movie is playing, however little disk wastage
   Block index (if frames are not split across
    blocks): need low RAM usage, but major disk
    wastage – internal disk fragmentation
   Block index(if frames are split across blocks):
    need low Ram usage, no disk wastage, extra
    seek times


                       CS 414 - Spring 2011
    Efficient VOD Service Techniques
   Problem:
          VOD service offers a large selection of videos from which customers can
           choose – want to offer low access latency for customers
   Main Challenge:
          How to handle large number of customers, maintain low cost of operation
           and at the same time provide acceptable access latency
   Caching
          Source: Caching Techniques for Streaming Multimedia over the Internet,
           Markus Hofmann, Eugene Ng, Katherine Guo, Sanjoy Paul, Hui Zhang
   Batching
          Source: Selecting among Replicated Batching VOD Servers, Meng Guo, Mustafa
           Ammar, E. Zegura

   Patching
          Source: Hierarchical Video Patching with Optimal Server Bandwidth, H.
           Hlavacs, S. Buchinger
                                     CS 414 - Spring 2011
Conclusion
 Designers of VOD systems strive to
  achieve low access latency for customers
 Challenges:
     Handle  large amount of customers (clients)
     Maintain low cost of operation
     Provide acceptable access latency




                      CS 414 - Spring 2011

				
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