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Current Work on Video Coding. Raj Kumar. Overview. Fine-Grained Scalability (FGS) What is it and why do we need it What are its drawbacks Our new scheme (FGS+) B-Frame only scheme All-Frame Scheme Future Directions. Enhancement Layer. I. B. B. P. B. Base Layer.

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Presentation Transcript
overview
Overview
  • Fine-Grained Scalability (FGS)
    • What is it and why do we need it
    • What are its drawbacks
  • Our new scheme (FGS+)
    • B-Frame only scheme
    • All-Frame Scheme
  • Future Directions
fine grained scalability

Enhancement Layer

I

B

B

P

B

Base Layer

Fine Grained Scalability
  • What is it
  • What are the pros and cons
traditional vs fine grained encoding

I

B

B

P

B

Enhancement Layer

I

B

B

P

B

Base Layer

Traditional Vs Fine-grained Encoding
temporal fgs

Temporal Enhancement Layer

Spatial Enhancement Layer

I

P

Base Layer

Temporal FGS
problem with temporal fgs
Problem with Temporal FGS
  • Reference Frames are poor quality
  • Doesn’t use motion-prediction well
  • Compression ratio suffers compared to traditional encoders (approx 2-2.5 DB)
insight
Insight
  • FGS provides two degrees of freedom
    • SNR
    • Temporal
  • Is there an optimal path that will maximize overall quality.
    • How do we determine it
    • How do we take advantage of it
slide8
Idea
  • Can we use a part of the enhancement layer, in addition to the base layer, to predict motion?
  • We can if we know how much of the base layer will be present at the decoder when the temporal layers are introduced
  • So if we build in rules about when temporal layers are introduced relative to spatial quality, we can!
implementation
Implementation
  • Increase SNR quality to a predetermined point
  • Then improve temporal quality
  • Further improve SNR quality at the new frame-rate
  • And so on….
fgs scheme b frame only

Temporal Enhancement Layer

Spatial Enhancement Layer

I

P

Base Layer

FGS+ Scheme (B-frame only)
two issues
Two issues
  • When (at what SNR quality) do we introduce new temporal-frames?
  • How much extended-reference do we use
introducing temporal frames
Introducing Temporal Frames
  • We conducted a study where users chose preferred frame-rate at different bit-rates:
  • As the bit-rate goes up, people prefer better frame-rates
  • High-motion videos (Stefan, Coastguard) require a quicker transition
determining the size of the reference
Determining the size of the reference
  • Plot SNR performance as a function of enhancement at various bit-rates
  • Choose enhancement corresponding to best quality
performance
Performance
  • Improvement over FGS varies from 0.19 dB to 1.28 dB
  • At low bit-rates simple videos benefit (Coastguard)
  • At high bit-rates complex videos benefit (Mobile)
fgs for all frames
FGS+ for All-Frames
  • We can improve performance further by using enhancement for base-layer P-frames also
  • But P-frames are present at all bit-rates. How much enhancement do we use?
fgs scheme all frames
FGS+ Scheme (All-frames)

Temporal Enhancement Layer

Spatial Enhancement Layer

I

P

Base Layer

improvement in performance
Improvement in Performance
  • At 3 bit-planes
  • Performance varies from –0.03 dB to 0.59 dB
  • Performance will degrade at low bit-rates, due to incomplete references
conclusion
Conclusion
  • FGS+ uses a spatio-temporal notion of video-quality
  • Improves performance of traditional FGS from 0.16 to 1.61 dB
current issues
Current Issues
  • Spatio-Temporal preference curves vary for different videos
  • How do we choose the correct curve automatically
  • Use Motion-Vectors, Image-Complexity
future directions
Future Directions
  • Factors other than video-characteristics do affect spatio-temporal preferences
    • Environment (resolution, display-type, lighting)
    • User preferences (moods, some prefer spatial-quality always)
  • How do we account for these other dimensions ?
  • Large dimensional space requires many (thousands) of sample points
future directions1
Future Directions
  • Build online experiment
    • Interactive web-based tool that lets user watch many videos
    • Allow user to change spatio-temporal settings
    • Record data corresponding to changes (video-characteristics, display resolution and type, user information)