CS Spring 2011 CS 414 – Multimedia Systems Design Lecture 28 – Media Server (Part 4) Klara Nahrstedt 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 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 Spring 2011

Some Facts Flickr – image and video hosting website In September 2010,  Fickr hosted 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 Spring 2011

Outline Multimedia File System  File allocation tables/Index tables  Additional File System Operations  Block sizes Efficient Video-on-Demand Service Techniques  Caching  Patching  Batching CS 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  Retrieval of a movie requires processing and synch of audio and video streams CS 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 Spring 2011

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

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 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 3 rd, or 5 th 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 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, text) belonging to this time frame CS Spring 2011 AV VT Frame index Movie Time line AV VT ……… V A V

Block Size Issues Large Block Size  Use large 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 CS Spring 2011 AV V V AAA V VV Block Index

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 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 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 Spring 2011