Kyoungwoo Lee, Minyoung Kim, Nikil Dutt, and Nalini Venkatasubramanian

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

• 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

Network
Mobile Video Applications
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Active Error Exploitation
Network

• 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

• 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

Mobile Video Application
Enc
Tx
Dec
Rx
CPU
WNI
CPU
WNI

• FDT Frame Drop Type
• Enc Encoding, Dec Decoding
• WNI Wireless Network Interface

FDT-1
FDT-2
FDT-3
Packet Loss
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Inherent Error-Tolerance of Video Data

• 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

Mobile Video Encoding
ME
DCT
Q
EE
ME Motion Estimation DCT Discrete Cosine
Transform Q Quantization EE Entropy Encoding
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Frame Losses due to Packet Losses
Mobile Video Applications
f3
f2
f1
Error-Prone Network
f4 is lost
Error-Induced Video Data

• 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

• 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)

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Energy Efficiency
f3
f2
f1
Error-Prone Network
f4 is lost
Error-Induced Video Data

• 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

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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

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Error-Resilient Video Encoder
Error-Resilient Video Encoder
Error- Resilient Video Data
Original Video Data
Error-Resilient Encoder
Parameters
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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
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Intentional Frame Dropping and PBPAIR

• Quality Management
• Error-Resilience
• (e.g.) EE-PBPAIR encodes video data resilient
  against f2 and f4
• Error-Tolerance

• Energy Efficiency
• Frame Dropping
• (e.g.) f2 is dropped
• PBPAIR

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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)

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

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Extended Tradeoff Space

• PLR 5 and EIR 0 to 50

EE-PBPAIR extends interesting tradeoff spaces
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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

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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_at_ics.uci.edu

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Backup Slides
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Intentional Frame Drop and Packet Loss
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EE-PBPAIR
Packet Loss
Intentional frame drop
Error-Exploiting Video Encoder
Error- Resilient Video
Error- Aware Video
Original Video
Error-Resilient Encoder (e.g., PBPAIR)
Error-Controller (e.g., frame dropping)
EIR
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Error Controller
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Error-Concealment
f3
f2
f1
Error-Prone Network
f4 is lost
Error-Induced Video Data

• 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
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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
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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
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System Prototype NS2
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Adaptive EE-PBPAIR