In this paper, we present a rate-distortion analysis for a distributed video coding system, which allows for the selection of a suitable quantization parameter for the H.264 coded key frames, under rate constraints. On the other hand, an adaptive rate allocation and quantization algorithm with a frame dropping strategy is used for the transmission of Wyner-Ziv frames in a multi-user scenario, without the need for a permanent feedback channel. The available bandwidth is dynamically shared between Wyner-Ziv and Key frames. Turbo-codes are used for the joint source-channel coding of the Wyner-Ziv frames and for the protection of the H.264 bitstream from channel errors. Simulation results show the superior performance of the proposed technique, compared to traditional systems with fixed quantization parameters and compression rates.