KIANOOSH MOKHTARIAN SCHOOL OF COMPUTING SCIENCE SIMON 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 High heterogeneity among receivers  Connection quality  Display resolution  Processing power Simulcasting

Motivation High heterogeneity among receivers  Connection quality  Display resolution  Processing power Simulcasting Transcoding

Motivation High heterogeneity among receivers  Connection quality  Display resolution  Processing power Simulcasting Transcoding Scalability  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 Temporal scalability Spatial scalability Quality scalability Conclusion

Temporal Scalability Enabled by restricting motion-compensated prediction

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

Temporal Scalability 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

Temporal Scalability: Hierarchical Pred’ Struct’ Non-dyadic case

Temporal Scalability: Hierarchical Pred’ Struct’ 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

Temporal Scalability: Hierarchical Pred’ Struct’ 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  QP T = QP T  High PSNR fluctuations inside a GoP  Subjectively shown to be temporally smooth

Temporal Scalability: Coding Efficiency Dyadic hierarchical B-pictures, no delay constraint

Temporal Scalability: Coding Efficiency High-delay test set, CIF 30Hz, 34dB, compared to IPPP

Temporal Scalability: Coding Efficiency 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 Temporal scalability Spatial scalability Quality scalability Conclusion

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

Spatial Scalability Motion-compensated prediction and intra-prediction in each spatial layer, as for single-layer coding  Inter-layer prediction

Spatial Scalability Motion-compensated prediction and intra-prediction in each spatial layer, as for single-layer coding  Inter-layer prediction  Same coding order for all layers

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

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

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

Spatial Scalability: Inter-Layer Prediction A new macroblock type signalled by base mode flag  Only a residual signal is transmitted  No intra-prediction mode or motion parameter

Spatial Scalability: Inter-Layer Prediction 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

Spatial Scalability: Inter-Layer Prediction 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

Spatial Scalability: Inter-Layer Prediction 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

Spatial Scalability: Inter-Layer Prediction For a 16x16 macroblock in an enhancement layer: 1 base mode flag 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 simulcast Base/enhancement layer at 352x288 / 704x576 Only the first frame is intra-coded Inter-layer prediction (ILP):  Intra (I), motion (M), residual (R)

Spatial Scalability: Coding Efficiency Comparison to single-layer coding and simulcast Base/enhancement layer at 352x288 / 704x576 Only the first frame is intra-coded Inter-layer prediction (ILP):  Intra (I), motion (M), residual (R)

Spatial Scalability: Coding Efficiency Comparison to single-layer coding and simulcast Base/enhancement layer at 352x288 / 704x576 Only the first frame is intra-coded Inter-layer prediction (ILP):  Intra (I), motion (M), residual (R)

Spatial Scalability: Coding Efficiency Comparison of fully featured SVC “single-loop ILP (I, M, R)” to scalable profiles of previous standards “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

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

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 Improved multi-layer encoder control  Optimized for both layers

Spatial Scalability: Encoder Control QP enhancement layer = QP base layer + 4 Hierarchical 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 Temporal scalability 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

Quality Scalability: MGS MGS: flexibility of the stream  Enhancement layer transform coefficients can be distributed among several slices  Packet-level quality scalability

Quality Scalability: MGS MGS: error robustness vs. coding efficiency

Quality Scalability: MGS 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 layer adapt. BL/EL control: use of key pictures

Quality Scalability: Coding Efficiency MGS vs. CGS

Overview Background Temporal scalability Spatial scalability Quality scalability 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 T.Wiegand, G. Sullivan, J. Reichel, H. Schwarz, and M.Wien, "Joint Draft ITU-T Rec. H.264 | ISO/IEC / Amd.3 Scalable video coding," Joint Video Team, Doc. JVT-X201, July H. Kirchhoffer, H. Schwarz, and T. Wiegand, "CE1: Simplified FGS," Joint Video Team, Doc. JVT-W090, April 2007.