1. Saving Bitrate vs. Users: Where is the Break-Even Point in Mobile Video Quality? ACM MM’11 Presenter: Piggy Date: 2012.05.07

2. Outline O Introduction O Related Work O User Study O Result O Discussion and Conclusion

3. Introduction O Mobile video service is getting popular O Due to the development of mobile device O Minimizing video bitrate is important O Wireless networks prefer low bitrate to adapt to different bandwidth conditions O Users prefer low bitrate as most network providers normally charge for data usage O Video providers need to save costs associated with serving the content

4. Introduction O However…… O Low video bitrate => poor video quality O Fortunately…… O Nonlinear relationship between perceived quality and video bitrate

5. Introduction O Goal: To find the most efficient bitrate requirement that O Optimizes bandwidth usage O Maintains good user viewing experience O Lowest acceptable video quality vs. lowest quality for long term viewing

6. Introduction O Contribution O Mapping of video bitrates to the subjective judgment of quality pleasantness O Impact of content type, video encoding parameters and user profile on mobile video viewing experience O Users’ selection processes and their criteria for the lowest pleasing quality for different content type

7. Related Work O Users’ requirements for mobile video depends on O Social and psychological factors O Consumption model, service, user profile, context, etc… O Video quality O Spatial and temporal resolution O Quantization O Motion and texture complexity

8. Related Work O Factors influence the reduction of bitrate O Resolution O Frame rate O Quantization O And the degradation in perceived video quality is not proportionate to the decrease in bitrate

9. Related Work O Subjective assessment O ITU recommendation: scale-based subjective assessment O 5/9/11-sclaes O Overburdens participants O Binary choice method for assessing acceptability

10. Related Work O Though previous works have identified the lowest acceptable quality level O They were restricted by the technology and device at that time. O Different resolution O People behaviors have changed (got used to HD quality)

11. User Study O Equipment O iPhone 3GS with 16GB storage O Display: 480x320 pixels O H.264/AVC O Up to 1.5 Mbps, 640x480 pixels, and 30 frames per second O AAC-LC audio format O Up to 150 kbps, 48kHz

12. User Study O Test material - 5 content types O News, music, animation, sports and movie

13. User Study O Test material – encoding using 3 parameters O Quantization parameters (QP) O Spatial resolution (SR) O 320x240, 480x320, and 640x480 O Frame rate (FR) O Divided into 3 groups based on SR:L, M and H with each group contain 10 test clips O 30 test clips for each content type

14. User Study O Total 150 test clips O 30x5

15. User Study O Participants O Lounge area outside of a university library O 40 participants O Equal number of males and females O Age range: 17 ~ 35 (average = 23.2) O User profile collection O Experience of using mobile video O Preference for content types

16. User Study O Participants’ profile

17. User Study O Procedure O Scenario explanation O 3 steps within 20-25 mins for data collection O Participant’s profile collection O Participant randomly chose the video contents O A short interview

18. User Study O Customized iPhone application O Participant profile collection O Content type choice O History review O Quality adjustment O Ascending O Descending

19. User Study

21. O Interview O What criteria did you use to select the desired video quality? O Is there any difference between your criteria for different content type? Why?

22. Result O Acceptability calculation O Lower than the selected lowest acceptable clip => 0 O Otherwise => 1 O Refers to the percentage of participants accepting a video quality as the lowest quality O Binary Logistic Regression O Video encoding parameters O Content type O Viewing order O User profile

23. Acceptability and Encoding Parameters O Different from O Content to content O Resolution to resolution O Movie is the lowest while new is the highest O The difference reduces as the resolution increases

24. Acceptability and Encoding Parameters

25. O Acceptability group O 0 – 40% should be avoided O 41 – 60% critical state O 61 – 80% can please users O 81 – 100% high user satisfaction

26. Acceptability and Encoding Parameters O Bitrate-acceptability curves

27. Acceptability and Encoding Parameters O Bitrate-acceptability curves

28. Acceptability and Encoding Parameters O Bitrate-acceptability curves O High resolution needs a higher bitrate O The acceptability of “sport” rises slower than other content types O Mapping of bitrate to acceptability

29. Influencing factors on quality Acceptability O Significant factors O Quantization parameter O Spatial resolution O Frame rate O Content type O Gender O Frequency O Duration O Viewing order O Non-significant factors O Age

30. Influencing factors on quality Acceptability O Effect of content type O Movie vs. music, news, and animation O Spatial resolution decreases => content type more significant O Effect of encoding parameters O Video quality increases with O Decrease of QP (great difference among adjacent QP values) O Increase of SR O Increase of FR

31. Influencing factors on quality Acceptability O Effect of viewing order O Acceptability in descending order is lower than ascending order O Significant for animation, music, news and sports but not for movie

32. Influencing factors on quality Acceptability O Effect of user profile

33. Influencing factors on quality Acceptability O Effect of user profile O Gender vs. frequency

34. Influencing factors on quality Acceptability O Effect of user profile O duration vs. frequency

35. Influencing factors on quality Acceptability O Effect of user profile O Users’ preference

36. Quality selection patterns O Average time spent on switching is different from content type to content type O News is the lowest

37. Quality selection patterns O Two selection patterns O Directly choose the target qualities without hesitation – mostly in ascending order O Bounced to and from the lower of higher quality for comparison – mostly in descending order

38. Criteria of acceptability quality O Users have different assessment criteria for different content types O Movie – high quality required (HD quality) O News – audio quality and sync. O Music – audio quality O Animation – fewer requirement O Sport – higher quality needed when small objects appear O Users’ preference leads to different result on the same content type O Ex: sport and news

39. Discussion and Conclusion O Users’ profile matters O The result is different from previous works O Exact required bitrate still depends on individual video, here only gives a estimated range O Platform dependency as well as video codecs O Fixed vs. adjustable service? O Prediction model and optimal delivery strategy

40. The End O Thanks for your attention