A Survey on Video Transmission Techniques <s> B. Common RC Algorithms <s> A new rate control scheme is used to calculate the target bit rate for each frame based on a quadratic formulation of the rate distortion function. The distortion measure are assumed to be either the average quantization scale of a frame or mean square error. The rate distortion function is modeled as a second order function of the inverse of the distortion measure. We presented a closed form solution for the target bit allocation which applies to both the digital storage media (DSM) applications (e.g., MPEG-2) and very low bit rate (VLBR) applications (e.g., MPEG-4). We perform experiments on a wavelet-based coder to demonstrate the versatility of our scheme. Model parameters are estimated using statistical linear regression analysis. Since the estimation uses the past encoded frames of the same picture prediction type (I, P and B pictures), the proposed approach is a single pass rate control technique. For the MPEG-2 coder the fluctuations of the bit counts are significantly reduced by 20 percent to 65 percent in the standard deviation of the bit count while the picture quality remains the same. For the MPEG-4 VM coder, the PSNR is improved by almost one dB as compared to the best MPEG-4 VM rate control using exhaustive combinations of quantization scale parameters. <s> BIB001 </s> A Survey on Video Transmission Techniques <s> B. Common RC Algorithms <s> 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. <s> BIB002
Application of rate-distortion (R-D) technique to rate control can prevent the buffer from overflowing or avoid its underflow under limited bandwidth as well as obtain optimum video quality. Thus, estimation or modeling of R-D is a key problem that the video encoder must solve. R-D can be described by using distortion-quantization (D-Q) function or rate-quantization (R-Q) function of the video encoder BIB001 . The two functions are called by a joint name, i.e., R-D function. Currently, models that are commonly used in the fields of video RC and RDO include classical RC model, quadratic model, logarithmic model, domain model and mixed model etc BIB002 .