Peer-to-Peer (P2P) technologies provide efficient and low-cost delivery for commercial and user-generated content. Although a number of audio-visual content distribution services have been developed using P2P-based mechanisms, it is still a challenge to guarantee satisfactory user experience on high quality video streaming services due to the dynamic nature of P2P distribution. An objective assessment service is the key enabler of service quality monitoring and management. However, this complex task can not be achieved by any individual objective model that only captures a certain aspect of service quality. This paper introduces a multimodal quality evaluation framework that is specifically designed and implemented for the assessment of video streaming services in P2P-based IPTV systems. Results of initial experiments show the effectiveness of this framework.