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By Qian Deng
MobiUS: Enable Together-Viewing Video Experience across Two Mobile Devices
A New Better-Together Mobile Application
• Bigger Screen, Higher Resolution, Real-Time Playback
Content • Introduction
• Collaborative Half-frame Decoding
• Energy Efficiency Optimization
• System Architecture and Implementation
• Experimental Results and Evaluation
• Discussion and conclusion
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
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
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
Collaborative Half-frame Decoding• Two Fundamental Facts: • Later frame only depends on a previous reference• Highly skewed MV distribution
• Push-based CDC
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
Energy Efficiency Optimization
• Reduce 75% CDC traffic• Worst case, increase 7% computation• Multi-macroblock-wide guardband, reduce CDC traffic
marginally
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
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
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
Experimental Results and Evaluation• Decoding Speed
Experimental Results and Evaluation• Synchronization
Experimental Results and Evaluation• Energy Efficiency
• Half-frame lead to energy saving• WiFi consumes more than half energy
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
Thank You
Questions?
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