The goal of this work is to present a full-reference (FR) audio-visual quality metric. We performed three psychophysical experiments in order to obtain a better understanding of how audio and video components interact with each other and how these interactions affect the overall audio-visual quality. In experiment I, subjects evaluated the quality of videos (without any audio) compressed at different video bitrates. In experiment II, subjects evaluated the quality of audio (without any video) compressed at different audio bitrates. In experiment III, subjects evaluated the quality of videos (audio-visual signals), which had their audio and video components compressed at different bitrates. Based on the data gathered from these experiments, we obtain a set of subjective models for audio-visual quality. Inspired by these subjective models, we propose a set of FR audio-visual quality metrics composed of a combination of a video quality metric and an audio quality metric. The proposed metrics have good performance and present better results when compared to simple FR video quality metrics.