This paper presents a multipath multimedia transport protocol (MPMTP), which exploits path diversity over heterogeneous wireless networks. The goal of MPMTP is to provide a seamless high-quality video streaming service by using multiple wireless networks simultaneously. In MPMTP, systematic Raptor codes are adopted to mitigate video quality degradation caused by wireless channel errors as well as to alleviate a head-of-line blocking problem in multipath environments, and their encoding parameters such as code rate, symbol size, and the number of source symbols are determined on the fly by considering the wireless channel state, Raptor encoding and decoding complexity, and receiver buffer occupancy. Furthermore, MPMTP performs packet scheduling considering not only wireless network conditions but also packet payload characteristics for smooth video playback. The proposed MPMTP is fully implemented in a Linux kernel and examined over real wireless network environments.