Impact of Stalling on QoE for 360-degree Virtual Reality Videos

Currently, there has been significant attention towards 360-degree videos delivery and immersive technology like Virtual Reality (VR). Streaming 360^○ video in tile-based method faces stalling and border effect of mixed bitrate tile due to small playback buffer and spatial partition of video with different bitrates tile respectively, which tend to deteriorates the end users Quality of Experience (QoE) significantly. In this paper, we study the impact of various stalling events occurs in 360^○ VR video on users QoE in virtual reality. We also investigate the interaction between the stalling event and bitrate level. Besides, we analyze the impact of stalling on the users presence and immersion in a virtual environment. To aim this, we created a database of 360^○ video with 4K resolutions and encoded the videos in three different bitrate levels (1Mbps, 5Mbps, and 15Mbps). We then simulate the stalling events at the start and in the middle of the video to conduct a subjective experiment. The subjective study finds that there is a strong dependency between stalling and bitrate. Stalling always impact the QoE of 360-degree videos but the strength of this negative impact depends on the video bitrate level, and the adverse effect of stalling event is more profound when the bitrate level approaches to the high and low end.