kianoosh mokhtarian school of computing science simon fraser university 6/24/2007 overview of the...

KIANOOSH MOKHTARIAN

SCHOOL OF COMPUTING SCIENCESIMON FRASER UNIVERSITY

6/24/2007

Overview of the Scalable Video Coding Extension of the H.264/AVC Standard

Motivation

High heterogeneity among receivers Connection quality Display resolution Processing power

Motivation


Simulcasting

Motivation


SimulcastingTranscoding

Motivation


SimulcastingTranscodingScalability

H.262|MPEG-2, H.263, MPEG-4 Visual

Overview

Background

Temporal scalability

Spatial scalability

Quality scalability

Conclusion

Background

Scalability Temporal Spatial Quality (fidelity or SNR) Object-based and region-of-interest Hybrid

Background

Scalability Temporal Spatial Quality (fidelity or SNR) Object-based and region-of-interest Hybrid

Applications Encode once, decode many ways Unequal importance + unequal error protection Archiving in surveillance applications

Background

Requirements for a scalable video coding technique Similar coding efficiency to single-layer coding Little increase in decoding complexity Support of temporal, spatial, quality scalability Backward compatibility of the base layer Support of simple bitstream adaptations after encoding

Overview

Background


Spatial scalability

Quality scalability

Conclusion

Temporal Scalability

Enabled by restricting motion-compensated prediction


Enabled by restricting motion-compensated prediction Already provided by H.264/AVC


Enabled by restricting motion-compensated prediction Already provided by H.264/AVC

Hierarchical prediction structure Pictures of temporal enhancement layers: typically B-pictures Group of Pictures (GoP)

Temporal Scalability: Hierarchical Pred’ Struct’

Dyadic temporal enhancement layers


Non-dyadic case


Other flexibilities Multiple reference picture concept of H.264/AVC Reference picture can be in the same layer as the target frame Hierarchical prediction structure can be modified over time


Adjusting the structural delay

Temporal Scalability: Coding Efficiency

Highly dependent on quantization parameters Intuitively, higher fidelity for the temporal base layer pictures

How to choose QPs Expensive rate-distortion analysis QPT = QP0 + 3 + T

High PSNR fluctuations inside a GoP Subjectively shown to be temporally smooth


Dyadic hierarchical B-pictures, no delay constraint


High-delay test set, CIF 30Hz, 34dB, compared to IPPP


Low-delay test set, 365x288, 25-30Hz, 38dB, delay is constrained to be zero compared to IPPP

Temporal Scalability: Conclusion

Typically no negative impact on coding efficiency But also significant improvement, especially when higher

delays are tolerable Minor losses in coding efficiency are possible when low delay

is required

Overview

Background


Spatial scalability

Quality scalability

Conclusion

Spatial Scalability

Motion-compensated prediction and intra-prediction in each spatial layer, as for single-layer coding

Spatial Scalability


Inter-layer prediction

Spatial Scalability


Inter-layer prediction Same coding order for all layers

Spatial Scalability


Inter-layer prediction Same coding order for all layers

Access units

Spatial Scalability: Inter-Layer Prediction

Previous standards Inter-layer prediction by upsampling the reconstructed samples of the

lower layer signal Prediction signal formed by:

Upsampled lower layer signal Temporal prediction inside the enhancement layer Averaging both





Lower layer samples not necessarily the most suitable data for inter-layer prediction





Lower layer samples not necessarily the most suitable data for inter-layer prediction

Prediction of macroblock modes and associated motion parameters Prediction of the residual signal


A new macroblock type signalled by base mode flag Only a residual signal is transmitted No intra-prediction mode or motion parameter


A new macroblock type signalled by base mode flag Only a residual signal is transmitted No intra-prediction mode or motion parameter If the corresponding block in the reference layer is:

Intra-coded inter-layer intra prediction The reconstructed intra-signal of the reference layer is

upsampled as a predictor

Inter-coded inter-layer motion prediction Partitioning data are upsampled, reference indexes are copied,

and motion vectors are scaled up


Inter-layer motion prediction (for a 16x16, 16x8, 8x16, or 8x8 macroblock partition)

Reference indexes are copied Scaled motion vectors are used as motion vector predictors


Inter-layer motion prediction (for a 16x16, 16x8, 8x16, or 8x8 macroblock partition)

Reference indexes are copied Scaled motion vectors are used as motion vector predictors

Inter-layer residual prediction Can be used for any inter-coded macroblock, regardless of its

base mode flag or inter-layer motion prediction The residual signal of the reference layer is upsampled as a

predictor


For a 16x16 macroblock in an enhancement layer:

1

basemodeflag

0

Inter-layer intra prediction (samples values are predicted)

Inter-layer motion prediction (partitioning data, ref. indexes, and motion vectors are derived)

Inter-layer motion prediction (ref. indexes are derived, motion vectors are predicted)

No inter-layer motion prediction

Inter-layer residual prediction

No inter-layer residual prediction

Spatial Scalability: Generalizing

Not only dyadic

Enhancement layer may represent only a selected rectangular area of its reference layer picture

Enhancement layer may contain additional parts beyond the borders of its reference layer picture

Tools for spatial scalable coding of interlaced sources

Spatial Scalability: Complexity Constraints

Inter-layer intra-prediction is restricted Although coding efficiency is improved by generally allowing

this prediction mode

Each layer can be decoded by a single motion compensation loop, unlike previous coding standards

Spatial Scalability: Coding Efficiency

Comparison to single-layer coding and simulcastBase/enhancement layer at 352x288 / 704x576Only the first

frame isintra-coded

Inter-layerprediction (ILP):

Intra (I),motion (M),residual (R)

Spatial Scalability: Coding Efficiency

Comparison of fully featuredSVC “single-loop ILP (I, M, R)”to scalable profiles of previousstandards “multi-loop ILP (I)”

Spatial Scalability: Encoder Control

JSVM software encoder control Base layer coding parameters are optimized for that layer

only performance equal to single-layer H.264/AVC




Not necessarily suitable for an efficient enhancement layer coding




Not necessarily suitable for an efficient enhancement layer coding

Improved multi-layer encoder control Optimized for both layers


QPenhancement layer = QPbase layer + 4Hierarchical B-pictures, GoP size = 16

Bit-rate increase relative to single-layer for the same quality is always less than or equal to 10% for both layers

Overview

Background


Spatial scalability

Quality scalability

Conclusion

Quality Scalability

Special case of spatial scalability with identical picture sizes

No upsampling for inter-layer predictions

Inter-layer intra- and residual-prediction are directly performed in transform domain

Different qualities achieved by decreasing quantization step along the layers

Coarse-Grained Scalability (CGS) A few selected bitrates are supported in the scalable bitstream Quality scalability becomes less efficient when bitrate difference between

CGS layers gets smaller

Quality Scalability: MGS

Medium-Grained Scalability (MGS) improves: Flexibility of the stream

Packet-level quality scalability Error robustness

Controlling drift propagation Coding efficiency

Use of more information for temporal prediction


MGS: flexibility of the stream Enhancement layer transform coefficients can be distributed

among several slices

Packet-level quality scalability

1 1 2 32 2 3 42 3 3 43 3 4 4


MGS: error robustness vs. coding efficiency


MGS: error robustness vs. coding efficiency Pictures of the coarsest temporal layer are transmitted as key

pictures Only for them the base layer picture needs to be present in decoding

buffer Re-synchronization points for controlling drift propagation

All other pictures use the highest available quality picture of the reference frames for motion compensation

High coding efficiency

Quality Scalability: Encoding, Extracting

Encoder does not known what quality will be available in the decoder

Better to use highest quality references Should not be mistaken with open-loop coding

Bitstream extraction based on priority identifier of NAL units assigned by encoder

Quality Scalability: Coding Efficiency

BL-/EL-only control: motion compensation loop is closed at the base/enhancement layer

2-loop control: one motion compensation loop in each layeradapt. BL/EL control: use of key pictures

Quality Scalability: Coding Efficiency

MGS vs. CGS

Overview

Background


Spatial scalability

Quality scalability

Conclusion

Conclusion

SVC outperforms previous scalable video coding standards

Hierarchical B-pictures Inter-layer prediction MGS Key pictures

Thank You

Any Questions?

References

H. Schwarz, D. Marpe, and T. Wiegand, “Overview of the scalable video coding extension of the H.264/AVC standard,” IEEE Transactions on Circuits and Systems for Video Technology, vol. 17, no. 9, pp. 1103–1120, September 2007.

T.Wiegand, G. Sullivan, J. Reichel, H. Schwarz, and M.Wien, "Joint Draft ITU-T Rec. H.264 | ISO/IEC 14496-10 / Amd.3 Scalable video coding," Joint Video Team, Doc. JVT-X201, July 2007.

H. Kirchhoffer, H. Schwarz, and T. Wiegand, "CE1: Simplified FGS," Joint Video Team, Doc. JVT-W090, April 2007.

kianoosh mokhtarian school of computing science simon fraser university 6/24/2007 overview of the...

Documents

spatial layer

singlelayer coding slide

avc slide

temporal base layer

ippp slide

hybrid slide

visual slide

time slide