This paper presents a novel adaptation technique for optimisation of the source and error protection rates in response to varying channel conditions in wireless networks. The optimisation methodology is based on accurate modelling of video frame distortion at the encoder. An optimal value for the quantisation parameter is calculated for video frames based on these estimates, and then video packets are mapped to one of a number of different priority radio bearers, according to their expected distortion. The algorithm performance is demonstrated for object based MPEG-4 video transmission over a UMTS/FDD system. The results demonstrate that a significant performance gain is achieved with the proposed scheme, compared with the equal error protection scheme for video transmission over a fixed bandwidth channel.