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Error-Exploiting Video Encoder to Extend Energy/QoS Tradeoffs for Mobile Embedded Systems

Error-Exploiting Video Encoder to Extend Energy/QoS Tradeoffs for Mobile Embedded Systems. Kyoungwoo Lee, Minyoung Kim, Nikil Dutt, and Nalini Venkatasubramanian. Department of Computer Science University of California at Irvine. DIPES ’08 Strategy. 25 mins talk and 5 min QnA

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Error-Exploiting Video Encoder to Extend Energy/QoS Tradeoffs for Mobile Embedded Systems

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  1. Error-Exploiting Video Encoder to Extend Energy/QoS Tradeoffs for Mobile Embedded Systems Kyoungwoo Lee, Minyoung Kim, Nikil Dutt, and Nalini Venkatasubramanian Department of Computer Science University of California at Irvine

  2. DIPES ’08 Strategy • 25 mins talk and 5 min QnA • Very broad audience • 10 to 15 mins for motivation and problem background • High level presentation • Technical depth is not that high, and deep technical highlights are in the backup slides

  3. Outline • Motivation and Problem Statement • Our Solution • Experiments • Conclusion

  4. Energy Reduction is Essential Network Mobile Video Applications • Battery-Operated Mobile Embedded Systems • Energy reduction is essential in battery-operated mobile embedded systems • Mobile video applications demand high energy consumption • Complex video encoding algorithms incur high overheads in terms of performance and power

  5. Active Error Exploitation Network f4 f3 f2 f1 • Active Error Exploitation – Intentional Frame Dropping • Skip the expensive video encoding algorithm  Energy saving • Degrade the video quality • Inherent error-tolerance mitigates the impact of frame drops on video quality

  6. Frame Drop Types Mobile Video Application Enc Tx Rx Dec CPU WNI WNI CPU • FDT: Frame Drop Type • Enc: Encoding, Dec: Decoding • WNI: Wireless Network Interface FDT-1 FDT-2 FDT-3 Packet Loss Error-prone Networks Intentional Frame Drop (one way to actively exploit errors) can result in energy reduction for each operation FDT-1 affects the following components with respect to power, performance, and QoS in mobile video applications

  7. Inherent Error-Tolerance of Video Data Mobile Video Encoding EE DCT Q ME f4 f3 f2 f1 ME – Motion Estimation DCT – Discrete Cosine Transform Q – Quantization EE – Entropy Encoding • Error-Tolerance of Video Data • Spatial and temporal correlation among consecutive video frames • Lossy video encoding • (e.g.) High Quantization Scale • Energy Reduction and Error-Tolerance • Error-tolerance can be used for energy reduction • (e.g.) partial ME vs. Full ME • One frame loss may not be noticed by users • (e.g.) One frame loss out of 30 frames per second

  8. Frame Losses due to Packet Losses Mobile Video Applications f3 f2 f1 Error-Prone Network f4 is lost Error-Induced Video Data f4 f3 f2 f1 Inherent Error-Tolerance of Video Data Error-Resilient/Error-Concealment Techniques

  9. Error-Resilience f3 f2 f1 Error-Prone Network f4 is lost Error-Induced Video Data f4 f3 f2 f1 • Error-Resilient Techniques • Insert Intra-frames (I-frames) periodically • (e.g.) GOP-10 inserts I-frame every 10 P-frames • Intra Refresh video encoding techniques • (e.g.) PBPAIR (Probability Based Power Aware Intra Refresh) encodes video data resilient against 25% frame loss rate (1 frame out of 4 frames)

  10. Energy Efficiency f3 f2 f1 Error-Prone Network f4 is lost Error-Induced Video Data f4 f3 f2 f1 • Energy-efficient error-resilient video encodings • (e.g.) PBPAIR or Probability-Based Power Aware Intra Refresh [Kim, MCCR06] • It may improve not only the video quality but also energy consumption

  11. Outline • Motivation and Problem Statement • Our Solution • Error-Exploiting Video Encoding • EE-PBPAIR • Experiments • Conclusion

  12. Our Proposal • Error-exploiting video encoder • Intentional frame dropping + error-resilient video encoding • Extends the tradeoff space for energy consumption / QoS

  13. Error-Resilient Video Encoder Error-Resilient Video Encoder Error- Resilient Video Data Original Video Data Error-Resilient Encoder Parameters

  14. Error-Exploiting Video Encoder Error-Exploiting Video Encoder Error- Injected Video Data Error- Aware Video Data Original Video Data Error-Injecting Unit Error-Canceling Unit Error Controller Error-Resilient Encoder Constraints Parameters & Feedback

  15. Intentional Frame Dropping and PBPAIR f3 f1 Error-Prone Network f4 is lost f2 is dropped Error-Induced Video Data EE-PBPAIR Error-Canceling Unit Error-Injecting Unit Intentional Frame Dropping PBPAIR • Quality Management • Error-Resilience • (e.g.) EE-PBPAIR encodes video data resilient against f2 and f4 • Error-Tolerance f4 f3 f1 • Energy Efficiency • Frame Dropping • (e.g.) f2 is dropped • PBPAIR

  16. EIR – Error Injection Rate EE-PBPAIR Error- Aware Video Data Original Video Data Error-Injecting Unit Error-Canceling Unit Frame Dropping PBPAIR Quality Constraint and Quality Feedback Parameters EIR • EIR adjusts the rate of intentional frame dropping • EIR is translated for PBPAIR (considering it as PLR) • Feedback-based quality adjustment • High EIR increases energy saving but degrades video quality

  17. Outline • Motivation and Problem Statement • Our Solution • Experiments • Conclusion

  18. End-to-End Experimental Framework • End-to-End Experimental Framework • Mobile video applications such as video conferencing consist of mobile encoding, wireless(and wired) networks, and mobile decoding • They affect each other in terms of energy consumption and QoS • System Prototype and NS2 Simulator • System Prototype • Runs video encoding and decoding on system prototype emulating mobile devices, and returns video quality in PSNR • Estimates the energy consumption of a processor (CPU power) • NS2 • Network Simulator • Estimates the energy consumption of WNI (transmission power)

  19. Experimental Setup Mobile Video Decoding Mobile Video Encoding Encoder Transmit Transmit Encoder Network System Prototype System Prototype NS2 CPU energy for encoding video quality (packet loss) CPU energy for encoding video quality (frame drop) WNI energy for transmit WNI energy for receive

  20. Evaluation • Video Encoding • GOP-K • PBPAIR • EE-PBPAIR • Energy Consumption • Enc EC (Energy Consumption for Encoding) + Tx EC (Energy Consumption for Transmission) • Rx EC (Energy Consumption for Receiving) + Dec EC (Energy Consumption for Decoding) • Video Quality • Video Quality at encoder after intentional frame dropping • Video Quality at decoder after packet losses in networks

  21. Experimental Results Energy Reduction from Active Error Exploitation Extended Energy/QoS Tradeoff

  22. Extended Tradeoff Space • PLR = 5% and EIR = 0% to 50% EE-PBPAIR extends interesting tradeoff spaces

  23. Energy Saving EC = Energy Consumption Enc EC = EC for Encoding Tx EC = EC for Transmission Dec EC = EC for Decoding Rx EC = EC for Receiving • PLR = 10% and EIR = 10% Energy saving occurs at every component in a path from encoding to decoding in mobile video applications • PSNR: Peak Signal to Noise Ratio

  24. Energy Reduction at QoS Cost At 10% cost of video quality, EE-PBPAIR can save the energy consumption of Enc and Tx by up to 49%

  25. Outline • Motivation and Problem Statement • Our Solution • Experiments • Conclusion

  26. Conclusion • Intentional Frame Drop is one way to exploit errors actively • Propose an error-aware video encoding (EE-PBPAIR) • Intentional frame dropping and the nature of energy-efficiency of PBPAIR reduces the energy consumption for video encoding • Present a knob (EIR) to adjust the amount of errors considering the QoS feedback • Maintain the video quality using error-resilience of PBPAIR • Future Work • Intelligent Frame Dropping Techniques • Extend Active Error Exploitation to the system level with error-aware architecture and network protocols in distributed embedded systems

  27. Thanks! Any Questions? kyoungwl@ics.uci.edu

  28. Backup Slides

  29. Intentional Frame Drop and Packet Loss Intentional frame drop Packet Loss Error-prone Networks

  30. EE-PBPAIR Intentional frame drop Packet Loss Error-Exploiting Video Encoder Error- Resilient Video Error- Aware Video Original Video Error-Controller (e.g., frame dropping) Error-Resilient Encoder (e.g., PBPAIR) EIR Error-prone Networks

  31. Error Controller

  32. Error-Concealment f3 f2 f1 Error-Prone Network f4 is lost Error-Induced Video Data f4 f3 f2 f1 • Error-Concealment Techniques • Interpolate the lost frame using near frames • Substitute the near frame for the lost one • (e.g.) f2 is copied for f3 (the lost one) in displaying frames

  33. GOP (Group of Picture) • Standard H.263 Video Encoder with varying IP-ratio • Higher IP-ratio generates more compressed video output, which consumes more energy Encoder GOP Intra Frame Static Constraint of Compression Rate IP-ratio (KNOB) Standard video encoding, which is unaware of energy consumption and error-resiliency

  34. PBPAIR • Proactively estimate the probability of the correctness, and adapt the intra_th (KNOB) based on the current network PLR (Packet Loss Rate) Encoder PBPAIR Intra MB PLR from Network Channel Intra_Th (KNOB) Error-Resilient Encoding, which can satisfy a given PSNR, and reduce the energy consumption for encoding

  35. EE-PBPAIR • EE-PBPAIR introduces another KNOB (intentional EIR) other than Intra_Th, and can further save the energy consumption Encoder EE-PBPAIR Intra MB PLR from Network Channel I-FS Intentional EIR (KNOB) Intra_Th (KNOB) Error-Introduced Video Encoding, which can still satisfy a given PSNR, and further maximize the energy saving compared to PBPAIR

  36. System Prototype + NS2

  37. Adaptive EE-PBPAIR

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