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?