saving bitrate vs. users: where is the break-even point in mobile video quality?
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Saving Bitrate vs. Users: Where is the Break-Even Point in
Mobile Video Quality?ACM MM’11
Presenter: PiggyDate: 2012.05.07
OutlineO Introduction
O Related Work
O User Study
O Result
O Discussion and Conclusion
IntroductionO Mobile video service is getting popular
O Due to the development of mobile device
O Minimizing video bitrate is importantO Wireless networks prefer low bitrate to
adapt to different bandwidth conditionsO Users prefer low bitrate as most network
providers normally charge for data usageO Video providers need to save costs
associated with serving the content
IntroductionO However……
O Low video bitrate => poor video quality
O Fortunately……O Nonlinear relationship between
perceived quality and video bitrate
IntroductionO Goal: To find the most efficient
bitrate requirement thatO Optimizes bandwidth usageO Maintains good user viewing
experience
O Lowest acceptable video quality vs. lowest quality for long term viewing
IntroductionO 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
Related WorkO Users’ requirements for mobile video
depends onO Social and psychological factors
O Consumption model, service, user profile, context, etc…
O Video qualityO Spatial and temporal resolutionO QuantizationO Motion and texture complexity
Related WorkO Factors influence the reduction of
bitrateO ResolutionO Frame rateO Quantization
O And the degradation in perceived video quality is not proportionate to the decrease in bitrate
Related WorkO Subjective assessment
O ITU recommendation: scale-based subjective assessmentO 5/9/11-sclaesO Overburdens participants
O Binary choice method for assessing acceptability
Related WorkO Though previous works have
identified the lowest acceptable quality levelO They were restricted by the
technology and device at that time.O Different resolutionO People behaviors have changed (got
used to HD quality)
User StudyO Equipment
O iPhone 3GS with 16GB storageO Display: 480x320 pixelsO H.264/AVC
O Up to 1.5 Mbps, 640x480 pixels, and 30 frames per second
O AAC-LC audio formatO Up to 150 kbps, 48kHz
User StudyO Test material - 5 content types
O News, music, animation, sports and movie
User StudyO Test material – encoding using 3
parametersO Quantization parameters (QP)O Spatial resolution (SR)
O 320x240, 480x320, and 640x480O Frame rate (FR)
O Divided into 3 groups based on SR:L, M and H with each group contain 10 test clipsO 30 test clips for each content type
User StudyO Total 150 test clips
O 30x5
User StudyO Participants
O Lounge area outside of a university library
O 40 participantsO Equal number of males and femalesO Age range: 17 ~ 35 (average = 23.2)
O User profile collectionO Experience of using mobile videoO Preference for content types
User StudyO Participants’ profile
User StudyO Procedure
O Scenario explanationO 3 steps within 20-25 mins for data
collectionO Participant’s profile collectionO Participant randomly chose the video
contentsO A short interview
User StudyO Customized iPhone application
O Participant profile collectionO Content type choiceO History reviewO Quality adjustment
O AscendingO Descending
User Study
User Study
User StudyO 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?
ResultO 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 RegressionO Video encoding parametersO Content typeO Viewing orderO User profile
Acceptability and Encoding Parameters
O Different fromO Content to contentO Resolution to resolution
O Movie is the lowest while new is the highest
O The difference reduces as the resolution increases
Acceptability and Encoding Parameters
Acceptability and Encoding Parameters
O Acceptability groupO 0 – 40% should be avoidedO 41 – 60% critical stateO 61 – 80% can please usersO 81 – 100% high user satisfaction
Acceptability and Encoding Parameters
O Bitrate-acceptability curves
Acceptability and Encoding Parameters
O Bitrate-acceptability curves
Acceptability and Encoding Parameters
O Bitrate-acceptability curvesO High resolution needs a higher
bitrateO The acceptability of “sport” rises
slower than other content typesO Mapping of bitrate to acceptability
Influencing factors on quality Acceptability
O Significant factorsO Quantization parameterO Spatial resolutionO Frame rateO Content typeO GenderO Frequency O DurationO Viewing order
O Non-significant factorsO Age
Influencing factors on quality Acceptability
O Effect of content typeO Movie vs. music, news, and animationO Spatial resolution decreases => content type
more significant
O Effect of encoding parametersO Video quality increases with
O Decrease of QP (great difference among adjacent QP values)
O Increase of SRO Increase of FR
Influencing factors on quality Acceptability
O Effect of viewing orderO Acceptability in descending order is
lower than ascending orderO Significant for animation, music, news
and sports but not for movie
Influencing factors on quality Acceptability
O Effect of user profile
Influencing factors on quality Acceptability
O Effect of user profileO Gender vs. frequency
Influencing factors on quality Acceptability
O Effect of user profileO duration vs. frequency
Influencing factors on quality Acceptability
O Effect of user profileO Users’ preference
Quality selection patterns
O Average time spent on switching is different from content type to content typeO News is the lowest
Quality selection patterns
O Two selection patternsO 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
Criteria of acceptability quality
O Users have different assessment criteria for different content typesO Movie – high quality required (HD quality)O News – audio quality and sync.O Music – audio qualityO Animation – fewer requirement O Sport – higher quality needed when small objects
appear
O Users’ preference leads to different result on the same content typeO Ex: sport and news
Discussion and Conclusion
O Users’ profile mattersO The result is different from previous worksO 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
The EndOThanks for your attention
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