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Study-Element Based Adaptation of Lecture Videos to Mobile Devices

Study-Element Based Adaptation of Lecture Videos to Mobile Devices. Ganesh Narayana Murthy (M.Tech IIT Bombay) Sridhar Iyer (Associate Professor, IIT Bombay). Problem Definition. Adapt CDEEP videos to be viewable on mobile devices: Viewable at low network bandwidths (like GPRS)

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Study-Element Based Adaptation of Lecture Videos to Mobile Devices

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  1. Study-Element Based Adaptation of Lecture Videos to Mobile Devices GaneshNarayana Murthy (M.Tech IIT Bombay) Sridhar Iyer (Associate Professor, IIT Bombay) NCC 2010, Chennai, 30/01/2010

  2. Problem Definition • Adapt CDEEP videos to be viewable on mobile devices: • Viewable at low network bandwidths (like GPRS) • Viewable at low cost • Video bit-rate • Size of video stream over time • Total size = bit-rate * total time • CDEEP video bit-rate: 1150kbps • GPRS bit-rate: 40kbps • The problem: • Video playing incurs delays if available network bandwidth is less than video-bit rate NCC 2010, Chennai, 30/01/2010

  3. Video Transcoding • Converting from one video format to another • Changing video bit rate • Changing other parameters like frame rate, screen resolution NCC 2010, Chennai, 30/01/2010

  4. Video Quality at low-bit rates (a) MPEG-1 (b) MPEG-2 Images from transcoded videos (Target bit rate : 40kbps, No audio) NCC 2010, Chennai, 30/01/2010

  5. Video Quality at low bit-rates (contd.) (d) H.263 (3gpp) (c) H.264 (mp4) Images from transcoded videos (Target bit rate : 40kbps, No audio) NCC 2010, Chennai, 30/01/2010

  6. (e) Flash Video (flv) Images from transcoded videos (Target bit rate : 40kbps, No audio) NCC 2010, Chennai, 30/01/2010

  7. Comparison of Video Codecs (Note: Video bit rate = 1150kbps, No audio, Target bit rate = 40kbps, No audio) Video Sizes are still high for viewing over GPRS NCC 2010, Chennai, 30/01/2010

  8. Study-Element Based Adaptation NCC 2010, Chennai, 30/01/2010

  9. Motivation • CDEEP video usually consists of • Presentation slides • Instructor explaining on white paper • Video of instructor talking • Presentation slide is usually not changing • Video of slide is not required. One image is sufficient • Idea • Extract one image every ‘n’ seconds and send to client. • This would reduce amount of data sent for showing one slide. NCC 2010, Chennai, 30/01/2010

  10. Method-1 • Send one image every ‘n’ seconds • Server sends one image every ‘n’ seconds to client • Audio is simultaneously streamed • Network bandwidth and Size • Network Overhead (NO) = Image Size / n • Size Overhead (SO) = Total size of images • What is the user experience? NCC 2010, Chennai, 30/01/2010

  11. User Experience Basis • Presentation Study Element • Portion of video showing one slide • White Paper Study Element • Portion of video showing instructor writing on white paper • Instructor Study Element • Portion of video showing instructor talking Presentation Slide White Paper ………….. ……….. 0 3 5 10 15 25 30 35 Video Time (secs) Delay in start of slide NCC 2010, Chennai, 30/01/2010

  12. User Experience • Presentation Element • Delay Experienced (D2) = • Delay in start of slide as compared to audio • White Paper Element • Delay Experienced (D1) = • Delay between any two consecutive images = Sending Rate • Instructor Element • Only audio important. No image need be sent. • User Experience is assumed to be one • User Experience (Ui) = 1 sec / Di NCC 2010, Chennai, 30/01/2010

  13. Method-2 • Trade-off for user experience • Cost incurred in terms of number of images sent • Same sending interval for all elements, cannot balance user experience and cost. • Choose different sending interval for each study element • Probably: • Higher user experience for white paper element • Lower user experience for presentation element Sending Interval User Experience Cost Trade-Off Relation NCC 2010, Chennai, 30/01/2010

  14. System Overview NCC 2010, Chennai, 30/01/2010

  15. Building the index • Corpus of 10 videos • Representative of various departments • Consider different sending intervals ‘r’ • For each ‘r’ find NO,SO and U for every study element in a video. • Repeat for all videos and take average. • This relation can be used backwards: • For calculating sending interval, given network bandwidth and user experience. NCC 2010, Chennai, 30/01/2010

  16. Graphs of User Experience NCC 2010, Chennai, 30/01/2010

  17. Graphs of overheads NCC 2010, Chennai, 30/01/2010

  18. Results Achieved Size Reduction Fig: Video stream size reduction (note: Original video bit-rate = 1150kbps, No audio) NCC 2010, Chennai, 30/01/2010

  19. Results (contd.) Balance User Experience and Cost Reduction in size user experience for white paper element remaining same Required Network Bandwidth =max(NO1,NO2) is reduced NCC 2010, Chennai, 30/01/2010

  20. Conclusion • Large size reduction can be achieved by using the concept of slideshows • Identifiying study-elements within the video helps define user-experience of the slideshow. • CDEEP Lecture videos can be adapted to low network bandwidths and in a cost-controlled manner. NCC 2010, Chennai, 30/01/2010

  21. Future Work Automated tagging • Identifying study element boundaries • Shot detection techniques User Experience Correlation • Identifying relation between obtained user experience and actual user values NCC 2010, Chennai, 30/01/2010

  22. References • H.264 white paper. http://ati.amd.com/products/pdf/h264_whitepaper.pdf. • Real-time Content-Based Adaptive Streaming of Sports Videos. Shih-Fu Chang, Di Zhong, and Raj Kumar. In CBAIVL '01: Proceedings of the IEEE Workshop on Content-based Access of Image and Video Libraries (CBAIVL'01), page 139, Washington, DC, USA, 2001. IEEE Computer Society. • Content-aware video adaptation under low-bitrate constraint. Ming-Ho Hsiao, Yi-Wen Chen, Hua-Tsung Chen, Kuan-Hung Chou, and Suh-Yin Lee. EURASIP J. Adv. Signal Process,2007(2):27-27, 2007. • A Characteristics-Based Bandwidth Reduction Technique for Pre-recorded Videos. WallapakTavanapong and SrikanthKrishnamohan. In IEEE International Conference on Multimedia and Expo (III), pages 1751-1754, 2000. NCC 2010, Chennai, 30/01/2010

  23. Questions? NCC 2010, Chennai, 30/01/2010

  24. Content-Aware Adaptation NCC 2010, Chennai, 30/01/2010

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