Rate-GOP Based Rate Control for
HEVC
S HA N S H E WA N G, S IW EI M A , S HIQI WA N G, D E B IN ZHAO, A N D W E N GAO
I E E E JO UR N A L O F S E L EC TED TO PI C S I N S I GN A L PRO C ES S ING, VO L . 7 , N O .
6 , D ECEM BER 2 0 1 3
Overview
 Introduction
 Hierarchical Rate Control Structure of Rate-GOP And Problem
Formulation
 Inter-frame Dependency Based Distortion Model And Rate Control
 R-Q Model And D-Q Model For HEVC
 Proposed Rate Control Algorithm Based on RDO
 Experiment Results
 Conclusions
Introduction
 In HEVC, many new coding tools are adopted to improve the coding performance, and they
bring great challenges to establish an accurate R-Q model and bit allocation scheme in rate
control for HEVC.
 To establish a more accurate R-Q model and a more efficient bit allocation scheme, the rate
control algorithm must consider the R-D characteristics.
 How to use the inter-frame dependency to improve the rate control performance is also a
difficult problem which may not be addressed well in the past.
Overview
 Introduction
 Hierarchical Rate Control Structure of Rate-GOP And Problem
Formulation
 Inter-frame Dependency Based Distortion Model And Rate Control
 R-Q Model And D-Q Model For HEVC
 Proposed Rate Control Algorithm Based on RDO
 Experiment Results
 Conclusions
Hierarchical Rate Control Structure And
Problem Formulation
1. Quad-tree Coding Structure And Reference Picture Set (RPS)
2. Proposed Hierarchical Rate Control Structure
3. Problem Formulation
Quad-tree Coding Structure
1. CU - LCU size = 64, maximum depth = 4
2. PU - NxN partition mode is allowed only
when the CU size is equal to minimum size
3. TU – TU is defined to represent the basic
unit for transform.
• Inter : the size of TU is independent
with the size of PU
• Intra : the size of TU cannot exceed the
size of PU
Reference Picture Set (RPS)
For RPS determination, it is composed of one frame with nearest temporal distance and three
frames with lowest QP in Decoded Picture Buffer.
Proposed Hierarchical Rate Control
Structure
 From Tables I and II and (1) and (2), it can be concluded that different frame in a Rate-GOP has
different influence on the following frames.
 Generally, the frame with QP+1 with relatively high reconstructed video quality will be referred
more than once and thus plays a crucial role, which is called the key frame. (POC %8==0)
*The four frames with the maximum depth will not be used as a reference frame,
so these are not included in the proposed structure.
Problem Formulation
Based on the proposed structure, the optimization problem can be
stated as follows:
Q and k is the number of frame in a GOP
Or :
Overview
 Introduction
 Hierarchical Rate Control Structure of Rate-GOP And Problem
Formulation
 Inter-frame Dependency Based Distortion Model And Rate Control
 R-Q Model And D-Q Model For HEVC
 Proposed Rate Control Algorithm Based on RDO
 Experiment Results
 Conclusions
Inter-frame Dependency Based
Distortion Model and Rate Control
Inter-frame prediction results in the distortion dependency and bit rate
dependency between a coding frame and its reference frames. (so we
analyze follow issues.)
 Inter-Frame Dependency Based Distortion Model
 Inter-Frame Dependency Based Rate Model
Distortion Model
The distortion of the coding frame has great dependency with its reference frames. This
kind of distortion dependency is one of the main factors affecting the bit allocation
scheme for rate control.
Rate Model
The bit rate dependency between the coding frame and its reference frame is also
investigated aiming at a deeper exploration for R-D relations.
Overview
 Introduction
 Hierarchical Rate Control Structure of Rate-GOP And Problem
Formulation
 Inter-frame Dependency Based Distortion Model And Rate Control
 R-Q Model And D-Q Model For HEVC
 Proposed Rate Control Algorithm Based on RDO
 Experiment Results
 Conclusions
R-Q Model For HEVC
 Generally speaking, R-Q model has great correlation with the distribution of the residual
information.
 It was stated in [25] that a single Laplacian distribution is not accurate enough to capture the
distribution due to the quad-tree coding structure. So a mixed distribution is applied below :
Nonzero coefficients of
CUs in j-th depth,
like P.6 mentioned.
 It has been proved in [12] that an accurate linear relation in ρ–domain between the bits and
the number of non-zero transformed coefficients holds firmly via the theoretical derivation for a
Laplacian distribution as follows:
[12] Z. He and S. Mitra, “Optimum bit allocation and accurate rate control for video coding via -domain source modeling,” IEEE Trans. Circuits
Syst. Video Technol., vol. 12, no. 10, pp. 840–849, Oct. 2002.
[25] B. M. Kim, “Modeling rates and distortion based on a mixture of laplacian distribution for inter-predicted residuals in quadtree coding
of HEVC,” IEEE Signal Process. Lett., vol. 18, no. 10, pp. 571–574, Oct. 2011.
R-Q Model For HEVC
According to the quantization in HEVC, for a certain j-th depth, the distortion 𝐷𝑗 (𝑞) can be
calculated by (12) and the percentage of zero coefficients 𝜌𝑖 (𝑞) can be computed by (13).
In [12], 𝐷 𝜌 = 𝜎 2 𝑒 −𝛼(1−𝜌)
R-Q Model For HEVC
Assume 𝑁𝑖,𝑗,𝑛𝑜𝑛_𝑧𝑒𝑟𝑜 and 𝑁𝑖,𝑗 denote the number of nonzero transformed coefficients and the
number of pixels of j-th depth in frame respectively. Combine with (13), we can get
Taylor expansion
D-Q Model For HEVC
 As illustrated in the above subsection, the linear relation between the bit rate and non-zero
transformed coefficients still holds firmly in HEVC under the mixed Laplacian distribution.
 For the first layer, the distortion can be represented by the following as stated in [12].
 For the second layer and third layer, we take into account the inter-frame dependency in (7) to
model the distortion as follows.
D-Q Model For HEVC
Subsequently, the distortion of a Rate-GOP can be presented as follows:
Overview
 Introduction
 Hierarchical Rate Control Structure of Rate-GOP And Problem
Formulation
 Inter-frame Dependency Based Distortion Model And Rate Control
 R-Q Model And D-Q Model For HEVC
 Proposed Rate Control Algorithm Based on RDO
 Experiment Results
 Conclusions
Proposed Rate Control Algorithm Based
on RDO
1.
Rate-GOP Level Bit Allocation
2.
Optimal Hierarchical Bit Allocation
3.
Header Bit Prediction
4.
Proposed Rate-GOP Based Rate Control Scheme
Rate-GOP Level Bit Allocation
 For GOP level, the target bits are allocated according to the bandwidth after coding the
previous GOP.
In order to get smoother bit rate, the really allocated bits is modified as
Optimal Hierarchical Bit Allocation
 For a Rate-GOP, given the bit budget 𝑅𝑇 allocated as in the previous subsection, the
optimization problem is to choose appropriate QPs to minimize the total distortion of the RateGOP.
 Combine with previous rate model in (21), distortion model in (26), (30) can be modified as
(21)
(26)
Optimal Hierarchical Bit Allocation
 By computing partial derivation with respect to 𝑞𝑖 ,
 From (18)
 Combine (20) and (34)
 By a Taylor expansion of (33) and (35)
Optimal Hierarchical Bit Allocation
 Taking (36) into (33), the bit rate for 𝑖-th frame can be obtain by
Once 𝜃𝑖 is determined by the correlation among adjacent frames, 𝑅𝑖 and QP can be obtained by
(20)
Optimal Hierarchical Bit Allocation
 To avoid the complicated calculation of 𝜔𝑖 in (39), 𝜔𝑖 is estimated from that of the previous
GOPs. Like (40)
𝑗-th layer in
𝑖-th GOP
𝛼𝑖,𝑗 is set to 0.5,0.3,0.2 initially
′
After encoding one Rate-GOP, if 𝑅𝑎𝑐𝑡𝑢𝑎𝑙 − 𝑇𝑟𝑎𝑡𝑒𝐺𝑂𝑃
≤ 𝑏𝑖𝑡𝑟𝑎𝑡𝑒/𝑓𝑟𝑎𝑚𝑒𝑟𝑎𝑡𝑒 , then the
weighting factors are calculated and utilized for the next Rate-GOP.
Proposed Rate-GOP Based Rate Control
Scheme
Header Bits Allocation
 Inspired by [10], in the experiments it was found that the header bits has strong linear
relationship with the number of PU and the value of MVD, as shown in Fig. 8.
Overview
 Introduction
 Hierarchical Rate Control Structure of Rate-GOP And Problem
Formulation
 Inter-frame Dependency Based Distortion Model And Rate Control
 R-Q Model And D-Q Model For HEVC
 Proposed Rate Control Algorithm Based on RDO
 Experiment Results
 Conclusions
Experiment Results
 The experiments are conducted on HEVC test model HM8.0.
 The test sequences and 6 testing configurations are detailed in [26].
A. Control accuracy
B.
R-D performance
C.
Complexity analysis
[26] F. Bossen, “Common test conditions and software reference configurations,” in Document: JCTVC-E700
Control Accuracy
The accuracy of bit mismatch is investigated in
terms of mismatch error as follows.
R-D Performance
The R-D performances in terms of BD-PSNR
and BD-Rate [27] results are presented for
comparison.
Firstly, experiments are conducted with the
proposed bit allocation scheme but without
using the proposed R-Q model.
R-D Performance
Secondly, experiments are implemented with
both the bit allocation scheme and the
proposed R-Q model.
As illustrated in Tables V–VII, the R-D
performances in terms of BD-PSNR and BDRate results are presented for comparison
with URQ algorithm and R-λ algorithm.
R-D Performance
Complexity Analysis
The parameters 𝑎𝑖 and 𝑏𝑖 in (20) are obtained
by linear regression.
The parameter 𝜃𝑖 in (20) are predicted from
the previous coded frames as in (38) to avoid
the complicated calculations.
The parameters α and β in (43) are also
obtained by linear regression.
The parameter 𝜔𝑖 in (39) is predicted from the
previous Rate-GOPs.
Overview
 Introduction
 Hierarchical Rate Control Structure of Rate-GOP And Problem
Formulation
 Inter-frame Dependency Based Distortion Model And Rate Control
 R-Q Model And D-Q Model For HEVC
 Proposed Rate Control Algorithm Based on RDO
 Experiment Results
 Conclusions
Conclusions
 The proposed rate control algorithm considered the Rate-GOP as a rate control unit and
provided a hierarchical structure for Rate-GOP.
 The inter-frame dependency based distortion model and bit rate model for Rate-GOP are
derived.
 Based on these models and a mixed Laplacian distribution of residual information, a new domain Rate-GOP based rate control is proposed.
 The experimental results demonstrated that the proposed algorithm can achieve much better
R-D performance than the two state of the art rate control algorithms for HEVC.