| 主权项 |
1. A method for determining coding parameters of a variable-resolution video stream by a video coder, said variable-resolution video stream comprising a plurality of resolution layers and being compressed to be transmitted at a plurality of given data bit rates or a plurality of given qualities through a heterogeneous network to a plurality of users, the method comprising:
generating reference charts with which to determine compression parameters, at least a quantization step, and/or protection parameters, at least a protection efficiency, as a function of a data bit rate and of a perceived quality; initializing parameters representative of said video coder, at least a maximum number Cmax of resolution layers, a minimum acceptable quality Dmin and a maximum achievable quality Dmax for each of said resolution layers; determining, for each user associated with a transmission link having an available bit rate di and a probability of error Pei, and for each available resolution Cj, a pair {data bit rate, protection efficiency} which offers a best perceived quality based on said reference charts; retaining, for each user, a resolution Cbest which offers the best perceived quality and representing said user in an x-axis plane equal to the data bit rate and y-axis plane equal to a total bit rate, which has a minimum value equal to the data bit rate divided by the protection efficiency; excluding from said representation users whose perceived quality value is below the minimum acceptable quality Dmin; evaluating a function f which links the data bit rate to the total bit rate based on the representation of said users; if the function f is strictly increasing for all users considered, then ranking the users in homogeneous groups according to the perceived quality, the users of one and the same group are associated with the same resolution Cbest; if the function f is not strictly increasing for at least two consecutive users, executing at least one of the following steps:
modifying a retained choice of the resolution layer for at least one of said users,replacing said users with a virtual user for which the total bit rate is equal to a lowest total bit rate of said users and for which the protection efficiency is equal to a minimum protection efficiency of said users, andeliminating from the ranking the user which has a highest total bit rate; determining, for each resolution layer of index i and in ascending order of a resolution level, compression parameters, at least a quantization step, and protection parameters, at least an efficiency of a correcting code, based on the reference charts, the quantization step being determined relative to a lowest available bit rate among the transmission links of a group of users to which said resolution layer of index i is assigned, the efficiency of the correcting code being determined as being a lowest efficiency among those allocated to the users of said group; compressing said video stream by applying said determined compression parameters; and protecting said video stream by applying said protection parameters to it. |
