CS 414 Multimedia Systems Design Lecture 28 Media

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

Administrative n MP 3 has ¨ Two options of MP 3 n Option 1 – 2 -way video chat: Linux – Android (eligible for competition) n Option 2 – 3 -way video conference: Linux-Linux n You should decide on one option (either option 1 or option 2)!!! ¨ April 29, 5 -7 pm, Google Competition for Option 1 solutions n Competition with judges via demos in SC 216 n Finalists will demonstration to judges between 5 -7 pm, April 29 n Finalists will prepare 5 minutes power point presentation ¨ April 27, 7 -9 pm, Preview of the MP 3 status n Wednesday, April 27, 7 -9 pm via demos in SC 216 in front of Prof. Nahrstedt and TA Shu n All groups show their status n Decision on which groups with option 1 will go towards Google competition CS 414 - Spring 2011

Administrative n MP 3 has April 29, Demonstration of projects (except of finalists) n Demos for grade between 2 -4: 30 pm in SC 216 to Prof. Nahrstedt and TA Shu Shi ¨ Sign-up sheet for demonstrations n Provided in class during week of April 22. ¨ April 29, midnight, code submission via compass n 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 n In September 2010, n ¨ Fickr hosted more than 5 billion images ¨ Developed by Ludicorp, Vancouver, 2004, now owned by Yahoo! n In August 2009, ¨ Flickr hosted 62 databases across 124 servers CS 414 - Spring 2011

Outline n Multimedia File System ¨ File allocation tables/Index tables ¨ Additional File System Operations ¨ Block sizes n Efficient Video-on-Demand Service Techniques ¨ Caching ¨ Patching ¨ Batching CS 414 - Spring 2011

Multimedia File Systems n Real-time Characteristics ¨ Read operation must be executed before well-defined deadline with small jitter n n Additional buffers smooth data File Size ¨ Can be very large even those compressed ¨ Files larger than 232 bytes n Multiple Correlated Data Streams ¨ Retrieval of 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) n For continuous files/contiguous placement n ¨ don’t n need maps For scattered files ¨ Need maps Linked lists (inefficient for multimedia files) n File allocation tables (FAT) n CS 414 - Spring 2011

Indexing and FAT Higher Level Index Table Per File I Frame P Frame B Frame P Frame ………. . File Allocation Table Block I 1 Location PTR Block I 2 Location PTR Block I 3 Location PTR Block P 11 Location PTR Block P 12 Location PTR Block B 1 Location PTR Block P 22 Location PTR …………. . CS 414 - Spring 2011

Constant and Real-time Retrieval of MM Data n n Retrieve index in real-time Retrieve block information from FAT Retrieve data from disk in real-time Real-time playback ¨ n Implement linked list Random seek (Fast Forward, Rewind) ¨ Implement n indexing MM File Maps ¨ include metadata about MM objects: creator of video, sync info CS 414 - Spring 2011

Fast Forward and Rewind (Implementation) n Play back media at higher rate ¨ n 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 ¨ n 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 n Small Block Sizes ¨ n n 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 ……… A V V A V T V CS 414 - Spring 2011 Frame index Movie Time line

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

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