by qian deng mobius: enable together-viewing video experience across two mobile devices
TRANSCRIPT
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By Qian Deng
MobiUS: Enable Together-Viewing Video Experience across Two Mobile Devices
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A New Better-Together Mobile Application
• Bigger Screen, Higher Resolution, Real-Time Playback
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Content • Introduction
• Collaborative Half-frame Decoding
• Energy Efficiency Optimization
• System Architecture and Implementation
• Experimental Results and Evaluation
• Discussion and conclusion
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Introduction• Assumption • The size of higher resolution video is about twice of device screen size• Two devices can communicate via high-speed local wireless networks• Two devices are homogeneous: same/similar software and hardware
capabilities
• Challenge • Real-time synchronous playback• Resource-constrained environment: limited battery life, memory, etc.• Dynamic adaption: expanding and shrinking video on two or one screen
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Collaborative Half-frame Decoding
scheme Comput. complexity
BW efficiency
Impl. complexity
Feasibility
Thin/C High/Low Worst Simple No
Thick/C High Bad Simple No
WTHD Low Bad Complex Possible
PTHD Low Good Complex Preferred
Full-Frame Decoding-based Approaches
Half-Frame Decoding-based Approaches
Energy Efficiency and Bandwidth Saving
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Collaborative Half-frame Decoding• Property of Video Coding• Temporal Correlation • Motion Compensated Prediction --- Motion Vector (MV)
• Problem • Cross-boundary reference
• Solution• Cross-device collaboration (CDC), • transmit the missing reference to each other
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Collaborative Half-frame Decoding• Two Fundamental Facts: • Later frame only depends on a previous reference• Highly skewed MV distribution
• Push-based CDC
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Energy Efficiency Optimization• Situation:• High bandwidth requirement for helping• Streaming data should be low enough for
multiple radio interfaces• More than 90% MVs are smaller than 16
• Solution:• Guardband-based collaborative half-frame decoding scheme
Only decode guardband blocks that will be referenced No guarantee the guardband to be correctly and completely decoded
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Energy Efficiency Optimization
• Reduce 75% CDC traffic• Worst case, increase 7% computation• Multi-macroblock-wide guardband, reduce CDC traffic
marginally
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System Architecture and Implementation• v
automatically set up a network between two mobile devices
Low Precision RequirementDetect arrival or departure of the other device
Check capability of new added deviceInform arrival and departure of other devices
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System Architecture and Implementation• RTT-based Synchronization Scheme
Host Device
Client Device
Wait Half RTT
Receive Notification
Display this frame
Next frame ready, Notify client
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System Architecture and Implementation
Frame: decoded framesLocal: bitstream for itselfNetwork: bitstream for otherHelp: CDC data
Two decoder modulesParser: divide into two half stream and extract MVs
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Experimental Results and Evaluation• Decoding Speed
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Experimental Results and Evaluation• Synchronization
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Experimental Results and Evaluation• Energy Efficiency
• Half-frame lead to energy saving• WiFi consumes more than half energy
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Discussion and conclusion• Discussion• Further Optimization Opportunities• Service Provisioning• User Study• Assumption on Homogeneity
• Conclusion• Expansion to more than two screens• Implementation on multiple radio interface• Realize real-time play on any divices
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Thank You
Questions?