This study seeks to establish under what conditions (mobility, network size, wireless channel) multi-source video streaming is feasible across a wireless vehicular ad hoc network (VANET). Overlay networks with multiple sources have proven to be robust, distributed solutions to multimedia transport, including streaming. To achieve video streaming over a VANET overlay, this study introduces a spatial partition of a video stream based on flexible macroblock ordering. Tests show this can achieve a gain of over 5 dB in video quality (PSNR) depending on video content and packet loss rates. However, routing of streamed services over multiple hops and multiple paths may lead to significant packet losses, resulting in unacceptable quality of service. The paper examines the impact of differing traffic densities and road layouts upon an overlay network's performance. The work modelled the emerging IEEE 802.11p for wireless VANETs. The research demonstrates that the vehicles' mobility pattern and their drivers' behaviour need to be carefully modelled to determine signal reception. The study also considers the impact of the wireless channel, which also should be more realistically modelled.