cs 414 - spring 2011 cs 414 – multimedia systems design lecture 28 – media server (part 4) klara...

CS 414 - 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


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


Some Facts

Flickr – image and video hosting website In September 2010,

Fickr hosted more than 5 billion imagesDeveloped by Ludicorp, Vancouver, 2004, now

owned by Yahoo! In August 2009,

Flickr hosted 62 databases across 124 servers


Outline

Multimedia File System File allocation tables/Index tablesAdditional File System OperationsBlock sizes

Efficient Video-on-Demand Service TechniquesCachingPatchingBatching


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 232 bytes

Multiple Correlated Data Streams Retrieval of a movie requires processing and synch of

audio and video streams


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)


Indexing and FAT


I Frame

Higher Level Index TablePer File

P Frame

B Frame

P Frame

Block I1 Location PTR



Block P11 Location PTR


Block B1 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


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


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


A V

V T

Frameindex

MovieTimeline

A V

V T

………

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


A V

V

V

A AA

V

VV

BlockIndex

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


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


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 cs 414 – multimedia systems design lecture 28 – media server (part 4) klara...

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