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  • A crawler (also called spider) is a program that automatically fetches Web pages. Most pages contain links to other pages. Therefore, a spider can start from almost any page and yet traverse a large number of diverse and distinct pages. Typically, used by search engines
  • multimedia-on-web.ppt

    1. 1. Characteristics of Streaming Media Stored on the Web <ul><li>M. Li, M. Claypool, R. Kinicki, and J. Nichols </li></ul><ul><li>To appear in ACM Transactions on Internet Technology , 2005. </li></ul>
    2. 2. Introduction (1/3) <ul><li>Several factors contribute to the growth of streaming media on the Web </li></ul><ul><ul><li>Availability of broadband </li></ul></ul><ul><ul><li>Desktop processing capabilities </li></ul></ul><ul><ul><li>Compression technology </li></ul></ul><ul><ul><li>Commercial interest </li></ul></ul><ul><li>E.g., RealNetworks estimated 350,000 hours of streaming media traffic (2001) </li></ul><ul><li>E.g., Significant fraction of Internet traffic (CAIDA, 2002) </li></ul>
    3. 3. Introduction – Related Work (2/3) <ul><li>Characterize streaming application performance (e.g., see references [10-16]) </li></ul><ul><li>“ TCP-friendly” streaming protocols (e.g., [4],[5]) </li></ul><ul><li>Queuing disciplines (e.g., [6-9]) </li></ul><ul><li>Acharya & Smith [19] studied all video URLs available in Alta Vista in 1997 </li></ul><ul><ul><li>Internet can not support real-time streaming </li></ul></ul>
    4. 4. Introduction – Research Questions (3/3) <ul><li>What are the most popular streaming media applications on the Web? </li></ul><ul><ul><li>Real, Windows, QuickTime, MPEG </li></ul></ul><ul><li>What is the ratio of streaming audio versus streaming video? </li></ul><ul><ul><li>Audio requires lower bitrates? </li></ul></ul><ul><li>Are media playback durations of stored media long-tailed? </li></ul><ul><li>What are typical streaming media bitrates? </li></ul><ul><ul><li>Indications of bandwidth requirements </li></ul></ul><ul><li>What fraction of streaming media codec's being used? </li></ul><ul><ul><li>Compression efficiency </li></ul></ul>
    5. 5. Methodology <ul><li>Develop a specialized Web crawler </li></ul><ul><li>Traverse 17 million URLs; </li></ul><ul><ul><li>Selected 17 Web pages as starting points </li></ul></ul><ul><ul><li>Considered popularity, demography, connectivity </li></ul></ul><ul><li>Identified ~ 30,000 media clips </li></ul><ul><ul><li>Used protocol information in URLS </li></ul></ul><ul><ul><li>E.g., rtsp://, mms:// etc </li></ul></ul><ul><li>Individually access media clips using custom built tools </li></ul><ul><ul><li>Encoding format, target bitrate, frame size, codec </li></ul></ul>
    6. 6. Analysis - Outline <ul><li>Aggregate analysis (Section III-A) </li></ul><ul><li>Commercial product analysis (Section III-B) </li></ul><ul><ul><li>Video </li></ul></ul><ul><ul><li>Audio </li></ul></ul><ul><li>Codec Analysis (Section III-C) </li></ul>
    7. 7. Aggregate Analysis <ul><li>Each spider collected 1 million URLs </li></ul><ul><ul><li>Approximately 11 million distinct URLs </li></ul></ul><ul><ul><li>About 55,000 streaming media URLs </li></ul></ul><ul><li>In 1997, 23,000 streaming media URLs in 25 million Web pages </li></ul><ul><ul><li>A five-fold increase in streaming! </li></ul></ul><ul><li>Fig 1: ~ 1% of the servers provide 100 or more media URLs per server </li></ul><ul><li>Fig 2: Real Media accounts for almost half of all the streaming media URLs </li></ul><ul><ul><li>QuickTime, AVI, MPEG were very popular in 1997, not any more! </li></ul></ul>
    8. 8. Commercial Product Analysis <ul><li>About 98% of the streaming media URLs are for pre-recorded media </li></ul><ul><li>Most audio/video clips are of short duration </li></ul><ul><ul><li>Median for audio ~ 4 minutes (a typical song) </li></ul></ul><ul><ul><li>Median for video ~ 2 minutes (a typical trailer) </li></ul></ul><ul><ul><li>In 1997, 90% of clips lasted 45 seconds or less </li></ul></ul><ul><ul><li>Duration still shorter than typical TV programs </li></ul></ul>5 1474 28 QuickTime 100 16545 12842 Total 32 6567 2591 Windows 63 8504 9863 Real Percentage Video Audio Media Type
    9. 9. Video/Audio Clips <ul><li>Median bitrate ~ 200Kbps </li></ul><ul><li>Approximately 70% of video targeted towards broadband connections; only 1% targets T1 </li></ul><ul><ul><li>In 1997, 20% videos were targeted at T1 </li></ul></ul><ul><li>Scalable streaming – multiple bitrates per stream </li></ul><ul><ul><li>About 12% of Windows Media streams use scalable streaming </li></ul></ul><ul><li>About 50% of the videos have less than 320x240 resolution – video resolutions are low </li></ul><ul><li>About 90% of the streaming audio is targeted for modem users </li></ul>
    10. 10. Media Codecs <ul><li>RealPlayer and Windows Media Player (latest version) buffer content at rates significantly higher than the playback rates </li></ul><ul><li>Raises “fairness” concern </li></ul>
    11. 11. Sampling Issues <ul><li>How are the results influenced if there are fewer crawler starting points? </li></ul><ul><li>How are the results influenced if there are fewer than 1 million URLs per starting point? </li></ul><ul><li>How does sampling affect distributions? </li></ul><ul><li>How does choice of starting points affect distributions? </li></ul>
    12. 12. Conclusions <ul><li>Streaming media on the Web increased 600% in the past 5 years </li></ul><ul><li>Real Media most popular, followed by Windows Media </li></ul><ul><li>Video and Audio are both equally popular </li></ul><ul><li>On-demand streaming dominates </li></ul><ul><li>Growth potential </li></ul><ul><ul><li>Better resolutions </li></ul></ul><ul><ul><li>Higher bitrates? </li></ul></ul>