In this paper we investigate the impact of a realistic physical layer on the H.264/AVC video transmission over Ad Hoc networks in urban environment. We propose a realistic Multilple Input Multiple Output (MIMO) physical layer which combines a determinist propagation model and a fine-grained model of wireless transmission errors. The determinist propagation model takes into account all the environmental characteristics (geometric and electric) and provides all the information of the multi-path channel (received power, complex impulse response). The wireless transmission errors model is based on a BER computation. The BER is calculated according to 802.11n standard to evaluate MIMO wireless links and, then, is compared to both SISO configuration and an existing wireless errors model using empirical propagation models. In the case of a SISO configuration, the BER is computed according to 802.11a standard. The simulation results show clearly a significant difference in term of QoS for the video transmission using realistic and empirical physical layer. In addition, the MIMO system, compared to a SISO one, improves the quality of links in the network and, thus, provides a better QoS for video transmission over Ad Hoc networks.