# Perceptual Quality of Audio-Visual Content with Common Video and Audio Degradations
## 2 Previous Work on Perceptual Quality Assessment

Table 1: Summary of subjective studies listed in Section 2. For audio content, a range of studies has focused on investigating the perceived quality effect of acoustic background noise [34; 35]. In the study presented by [PERSON] et al. [29], speech intelligibility was compared across different levels of background noise and syntactic structure complexity. Results suggested that intelligibility was more affected by background noise than syntactic complexity. In another study, [PERSON] et al. [30] explored the effects of several voice over IP (VolP) distortions. The dataset included speech samples impaired with background noise, competing speaker effects, clipping, echo, and chopped speech, all added in isolation. The authors reported that echo and background noise had a heavier impact on the quality perceived by participants. A recent study presented by [PERSON] et al. [31] investigated the stalling effect over music streaming. The authors state that music streaming consumption differs from a video streaming scenario since music is usually played in the background. In this study, the authors explored the perceived quality of users while they are performing other tasks. For speech enhancement, researchers have exploited the visual information available (e.g., lip movement, facial expression) to achieve stronger performance. Some relevant audio-visual speech datasets are listed in [36; 37; 38]. In terms of audio-visual quality, a number of studies have explored the audio and video interactions and their corresponding contribution to the perceived overall quality. Some of these studies showed that, for certain types of content, the video component has a stronger influence on the audio-visual quality. In contrast, the study presented in [20] reported that for certain communication scenarios (e.g., teleconference calls), the audio component plays a more important role in the overall perceived quality. In general, results in the literature show that the influence of the video and audio components on the perceived quality is related to several context factors (nature of experience, e.g., teleconference, sports events, movies, etc.). In addition, human and technological factors are also determinant to model the human perceived quality [39]. Aiming to study these factors and their influence, researchers have explored different experimental methodologies, new and diverse media content, and new types of distortions. For example, [PERSON] et al. [22] and [PERSON] et al. [23] have tried to capture the participants' attention by using long-duration audio-visual stimuli. Both studies applied alternative methodologies to collect human responses. [PERSON] et al. [25] conducted a group of experiments to study the impact of heavy audio and video compression artifacts on quality. Similarly, [PERSON] et al. [19] performed a study where ten different laboratories ran perceptual experiments, which consisted of presenting sequences with compressed audio and video components, considering different environments and devices. More recently, a study presented by [PERSON] et al. [18] conducted an audio-visual perceptual experiment introducing distortions caused by audio and video compression and video compression combined with video scaling. Despite their setup differences, all these three studies agreed on the influence of audio on the perceived audio-visual quality. However, a more specific perceptual study presented by [PERSON] et al. [32] explored the trade-off between audio and video quality over live music streaming sequences. The study applied distortions caused by audio and video compression for a mobile network environment. The study concluded that, for this particular case study, reducing the audio bitrate didn't affect the overall audio-visual quality and, the video bitrate reduction had a great impact on the perceived audio-visual quality. In another study, [PERSON] et al.