Minqiang Jiang

On Lagrange multiplier and quantizer adjustment for H.264 frame-layer video rate control

H.264/AVC encoder employs a complex mode-decision technique based on rate-distortion optimization. It calculates rate-distortion cost (RDcost) for all possible modes to choose the best one having the minimum RDcost. This paper presents a frame-layer rate control for H.264/AVC that computes the Lagrange multiplier (/spl lambda//sub MODE/) for mode decision by using a quantization parameter (QP) which may be different from that used for encoding. At the same time, we also compare actual bits produced by previous macroblocks (MBs) with the total bits allocated to these MBs to further modify /spl lambda//sub MODE/. The objective of these measures aims to produce bits as close to the frame target bits for rate control as possible. This is very important in the case of low-bit-rate tight buffer applications. In order to obtain an accurate QP for a frame, we employ a complexity-based bit-allocation scheme and a QP adjustment method. Simulation results comparing with the H.264 Joint Video Team (JVT) rate control method show that the H.264 encoder, using the proposed algorithm, achieves a visual quality improvement of about 0.56 dB, performs better for buffer overflow and underflow, and achieves a smaller PSNR deviation.

Improved frame-layer rate control for H.264 using MAD ratio

In recent years, rate control plays an increasing important role in real-time video communication applications using MPEG-4 AVC/H.264. An important step in many existing rate control algorithms, which employs the quadratic rate-distortion (R-D) model, is to determine the target bits for each P frame. This paper aims in improving video distortion, due to high motions or scene changes, by more accurately predicting frame complexity using the statistics of previously encoded frames. We use mean absolute difference (MAD) ratio as a measure for global frame encoding complexity. Bit budget is allocated to frames according to their MAD ratio, combined with the bits computed based on their buffer status. Simulation results show that the H.264 coder, using our proposed algorithm with virtually little computational complexity added, effectively alleviates PSNR surges and sharp drops for frames caused by high motions or scene changes.

Low-delay rate control for real-time H.264/AVC video coding

This paper presents an efficient rate control scheme for the H.264/AVC video coding in low-delay environments. In our scheme, we propose an enhancement to the buffer-status based H.264/AVC bit allocation method. The enhancement is by using a PSNR-based frame complexity estimation to improve the existing mean absolute difference based (MAD-based) complexity measure. Bit allocation to each frame is not just computed by encoder buffer status but also adjusted by a combined frame complexity measure. To prevent the buffer from undesirable overflow or underflow under small buffer size constraint in low delay environment,the computed quantization parameter (QP) for the current MB is adjusted based on actual encoding results at that point. We also propose to compare the bits produced by each mode with the average target bits per MB to dynamically modify Lagrange multiplier (/spl lambda//sub MODE/) for mode decision. The objective of QP and /spl lambda//sub MODE/ adjustment is to produce bits as close to the frame target as possible, which is especially important for low delay applications. Simulation results show that the H.264 coder, using our proposed scheme, obtains significant improvement for the mismatch ratio of target bits and actual bits in all testing cases, achieves a visual quality improvement of about 0.6 dB on the average, performs better for buffer overflow and underflow,and achieves a similar or smaller PSNR deviation.

An improved frame and macroblock layer bit allocation scheme for H.264 rate control

This paper proposes an improved frame and macroblock layer bit allocation scheme for H.264 rate control. Our improved algorithm has two main features: (a) a bit allocation method based on an improved complexity measure that uses a combination of mean absolute difference-based (MAD-based) measure and PSNR-based measure; and (b) a quantization parameter (QP) adjustment method and a better frame skipping decision method to improve overall visual quality and the accuracy of bit allocation. Simulation results show that our proposed algorithm effectively alleviates visual quality degradation and variation caused by high motion or scene changes. Our method is effective especially for low bit rate video streaming.

Frame layer bit allocation scheme for constant quality video

In order to achieve constant quality across the whole video sequence under the channel bandwidth and buffer constraints, it is necessary to allocate more bits to frames with scene changes or high complexity and fewer bits to low complexity frames. In this work, we propose a new frame layer bit allocation scheme for H.264 video coding using mean absolute difference (MAD) ratio, which is the ratio of MAD of current frame to the average MAD from the starting frame up to the previous frame in a GOP. We provide a theoretical justification of MAD ratio as a measure of frame complexity. Bit budget is allocated to frames according to their MAD ratios, combined with the bits computed based on their buffer status. Simulation results show that the H.264 coder, using our proposed algorithm with virtually little computational complexity added, effectively alleviates visual quality degradation caused by high motion or scene changes. Our proposed algorithm significantly reduces the standard deviation of PSNR, hence producing a nearly constant video quality throughout the whole video sequence, when compared with other existing video schemes

On enhancing H.264 rate control by PSNR-based frame complexity estimation

This work presents an enhancement to the frame layer buffer status-based H.264 rate control method. The enhancement is by using a PSNR-based frame complexity estimation to improve the existing mean absolute difference based (MAD-based) complexity measure. Bit allocation to each frame is not just computed by encoder buffer status but also adjusted by a combined frame complexity measure. Simulation results show that the H.264 encoder, using the proposed algorithm, can achieve better visual performance than that of the existing H.264 JVT rate control method (JVT/spl I.bar/G012).

Bit Allocation Scheme for Low-Delay H.264/AVC Rate Control

This paper presents an efficient rate control scheme for H.264/AVC video coding in low-delay environments. In our scheme, we propose a close-form solution to optimal bit allocation problem subject to constraints and we derive theoretically a mean absolute difference based (MAD-based) complexity measure. The complexity measure of the current macroblock is also used to predict SKIP mode such that the initial quantization parameter (QP) is determined directly. Initial QPs of other kind of macroblocks (MBs) are computed based on a conventional quadratic model. To prevent the buffer from undesirable overflow or underflow under small buffer size constraint, the obtained initial QP is further adjusted based on actual encoding results at that point. Simulation results show that the H.264 encoder, using our proposed scheme, achieves a visual quality improvement of about 0.65 dB on the average and performs better for buffer overflow and underflow.

Frame-layer H.264 rate control improvement using Lagrange multiplier and quantizer

The paper presents a frame-layer rate control for H.264 that computes the Lagrange multiplier (/spl lambda//sub MODE/) for mode decision by using a quantization parameter (QP) which may be different from that used for encoding. At the same time, we also compare the bits produced by each mode with the average target bits of each macroblock (MB) in a frame to modify /spl lambda//sub MODE/ further. The objective of these measures is to produce bits as close to the frame target bits as possible. In order to obtain an accurate QP for a frame, we employ a complexity-based bit allocation scheme and a QP adjustment method. Simulation results show that the H.264 encoder, using the proposed algorithm, controls the bit rate better, achieves a visual quality improvement of about 0.5 dB better than that of the existing H.264 rate control method (JVT-G012), with a smaller visual quality variation.

An approach to image compression using R-D optimal OMP selection

Transform-based coding is a technique that is widely used in image and video compression, where compression is achieved via decomposing each component block or patch over a complete dictionary known to provide compaction. Recently, there has been a growing interest in using basis selection algorithms for signal approximation and compression. Signal approximation using a linear combination of basis functions from an over-complete dictionary has proven to be an NP-hard problem. To solve this problem, Orthogonal Matching Pursuit (OMP) algorithm is often used to select dictionary elements and their coefficients. Based on its iterative nature, we propose a Rate-Distortion Optimization (RDO) method to select the number of nonzero coefficients assuming that a sparsity constraint is given. Experimental results demonstrate a very good improvement by our proposed method over conventional DCT based scheme.