With the development of wireless communication network, Vehicular Ad-hoc Network (VANET) has received considerable attentions. US Department of Transportation (USDOT) is piloting a deployment concept to encourage embedding and retrofitting vehicles with DSRC interface to support varieties of applications for both safety and non-safety purposes. In addition to traditional data service, many real-time video streaming applications are increasingly being developed over VANET. Although it is desirable to delivery the packets directly through single hop communications, such condition is not always available in the real environment. To support real-time video applications in VANET, we have to deeply understand their performance under multihop conditions and even with others' interference. To the best of our knowledge, no work has been done on measuring the multihop video streaming transmission performance with interference over real environment. In this paper, a DSRC device based test-bed is developed to investigate the performance of multihop real-time video streaming transmission and the impact of interference. To overcome the high packet loss rate which is a main shortage of video streaming transmission over VANET, we improve the application by adding retransmission and startup caching schemes. We also evaluate the performance of different retransmission strategies and analyze how to optimize the retransmission scheme for minimizing the number of collided and late packets based on the transmission rate of interference.