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This paper investigates multi-modal aspects of audiovisual quality assessment for interactive communication services. It shows how perceived auditory and visual qualities integrate to an overall audiovisual quality perception in different experimental contexts. Two audiovisual experiments are presented and provide experimental data for the present analysis. First, two experimental contexts are compared, i.e., passive 'viewing and listening' and interactive, with regard to their impact on the audiovisual qualities as subjectively perceived by the user. Second, the effects of cross-modal interactions on the assessment of the audio and video qualities are measured for those experimental contexts. The results are compared to the ones found in the literature revealing both similarities and differences in terms of magnitude and also in which cases they occur. Third, the impact of the conversational scenario on the assessment of the auditory and visual qualities is investigated. Finally, results from the literature related to audiovisual integration are gathered by the type of application. A general integration function is proposed for each category, and the performances of these 'application-oriented' models demonstrate a direct gain in prediction.

With the advent of audio-visual IP clients, video telephony becomes a realistic option in many application scenarios. In order to guarantee an adequate quality to its users, providers of audio-visual telephony services need to know the impact of the audio and video transmission channel characteristics on perceived Quality of Experience (QoE) in a realistic interactive setting. For this aim, a conversational video telephony experiment was conducted where the audio and video channel settings were adjusted in a controlled way, and participants were asked about the perceived audio, video and overall quality after carrying out a conversation over the audio-visual channel. We analyze the results with respect to the impact the two modalities have, as well as with respect to the impact of the conversation scenario.