Rate control plays a key role in video coding standards. Its goal is to achieve a good quality at a given target
bit-rate. In H.264/AVC, rate control algorithm for both Intra and Inter-frames suffers from some defects. In
the Intra-frame rate control, the initial quantization parameter (QP) is mainly adjusted according to a global
target bit-rate and length of GOP. This determination is inappropriate and generates errors in the whole of
video sequence. For Inter coding unit (Frame or Macroblock), the use of MAD (Mean Average Differences) as
a complexity measure, remains inefficient, resulting in improper QP values because the MAD handles locally
images characteristics. QP miscalculations may also result from the linear prediction model which assumes
similar complexity from coding unit to another. To overcome these defects, we propose in this paper, a new
Rate-Quantization (R-Q) model resulting from extensive experiments. This latter is divided into two models.
The first one is an Intra R-Q model used to determine an optimal initial quantization parameter for Intraframes.
The second one is an Inter R-Q model that aims at determining the QP of Inter coding unit according
to the statistics of the previous coded ones. It does not use any complexity measure and substitutes both
linear and quadratic models used in H.264/AVC rate controller. Objective and subjective simulations have been
carried out using JM15.0 reference software. Compared to this latter, the global R-Q model (Intra and Inter
models combined) improves the coding efficiency in terms of PSNR, objectively (up to +2.01dB), subjectively
(by psychophysical experiments) and in terms of computational complexity.