Peer-to-peer streaming of HD video over ad-hoc 802.11 wireless networks is a popular application, but the received video quality, and therefore the user's Quality of Experience (QoE), depends heavily on the condition of the wireless channel used. This paper presents Active Scanning-based Dynamic Channel Switching (ASDCS), which ensures wireless video streaming takes place over the channel whose condition is most likely to provide good received video quality. ASDCS selects an initial channel before video streaming begins, assesses the performance of the current channel during streaming, and dynamically searches for a better channel if the current one is insufficient. Our simulation results show that ASDCS outperforms existing static queue-threshold and SINR-based methods.