1 Introduction
As virtual reality (VR) acquisition and display systems become widely accessible, people are getting used to capturing, editing, and interacting with VR content, which is evidenced by the accelerated proliferation of videos uploaded to popular video sharing and social media platforms (e.g., Bilibili and Youtube). A practical issue arising from user-generated videos is that they come with complex visual artifacts (i.e., the so-called authentic distortions) from acquisition to processing stages [2]. Thus, understanding how people perceive video distortions in virtual environments is central to many VR-enabled video applications.