A Survey on Video Transmission Techniques <s> Quadratic R-D Model <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> BIB001 </s> A Survey on Video Transmission Techniques <s> Quadratic R-D Model <s> The joint scalable video model(JSVM)as a scalable extension of H.264/AVC provides a high efficient solution for scalable video coding(SVC).However,there is not efficient rate control scheme is specified.This paper presents a new rate control scheme for the JSVM based on the special structure of hierarchical B decomposition(or motion compensation temporal filtering(MCTF)).In a sense of bit allocation,a novel hierarchical bit allocation strategy is proposed.Meanwhile,the different rate-distortion(R-D)model is provided for each kind picture with different picture type or temporal decomposition level.Experiment results show that the mismatch of target bit rate and real bit rate generated for coding doesn't exceed 2%;meanwhile,the PSNR improvement can be up to 1dB in low bit rate;furthermore,comparing to the original rate control method which achieves the target bit rate through regulating quantization parameter(QP)step by step,the computation complexity of the proposed rate control algorithm base on experimental model is reduced drastically. <s> BIB002
By virtue of researches, Chiang et al. BIB002 put forward a quadratic video R-D model in 1997. Firstly, it is assumed that information source accords with Laplace distribution, code rate is R and distortion is D. The logarithmic form in (3) can be used to express the R-D model: Where is Laplace distribution parameter and >0. If we use Taylor to develop the foregoing formula, adopt quantization step to measure distortion and assume that R and Q are encoding bit number and quantization step, respectively, the R-D function about RC in the logarithmic form in the foregoing formula will be converted into an expression form of quadratic polynomial, as shown in BIB001 . The model is applied to MPEG-4 standard and obtains favorable RC effect.  In the foregoing formula, a 1 and a 2 are model parameters. However, Lee et al.  deem that texture information and non-texture information should be distinguished when image coding is carried out. However, the quadratic model does not consider texture information. If mean absolute difference (MAD) of signals is defined as frame difference between predicted image and the original one, content complexity of images can be measured by MAD. In doing so, the quadratic R-D model that is related to content complexity of images and describes texture information about encoding, can be obtained, as shown in the following: The model parameters a 1 and a 2 can be obtained by linear regression technique. When the parameters a 1 and a 2 are updated, ways to select sample data can be improved by prediction mechanism of encoding.