Time-Variant Visual Attention in 360-Degree Video Playback

The user visual attention has been playing an imperative role in visual Quality of Experience (QoE) modeling. In recent years, researchers have developed numerous visual attention models for images and videos. However, existing studies on visual attention generally perform on spatial domain (i.e. pictures) without consideration on time-variant user attention. Besides, the user attention on immersive video playback has not been well investigated in Virtual Reality (VR) environment. In this paper, we design subjective experiments to acquire the user attention during 360-degree video playback, in order to characterize the visual attention changes on time axis. We compare and model the temporal attentions in two scenarios: 360-degree video and conventional 2D video display. It is observed in video display, the user attention needs a short period (~ 30 seconds) to concentrate to a relatively stable level. Within this period, the user attention to 360-degree video is significantly lower than that to traditional 2D videos, which shows that the users are relatively difficult to adapt to VR display. Therefore, short videos less than 30 seconds, especially short 360-degree videos, are not preferable in subjective video quality assessment, although they have been tested in some scenarios. We hope this conclusion would conduce to QoE modeling during video display of VR environment.