# Subtitling 3D VR Content with Limited 6 DoF: Presentation Modes and Guiding Methods
## 1 Introduction  
All multimedia services must be accessible. This is required not only to adhere to global regulation frameworks, but also to ensure global e-inclusion and equal access to information [1]. In multimedia services, accessibility is typically provided by means of access services (e.g., subtitling, audio description, and sign language interpretation), appropriate interaction modalities (e.g., user interfaces, voice control), and assistive technologies (e.g., voice readers and content processing to address specific audiovisual impairments). The study in [1] provides statistics about the percentages of the global population with some form of audiovisual impairment, and about the ageing process, which is closely related to disability rates. These statistics reveal the significant percentage of the population with accessibility needs. Multimedia content includes audio and visual elements which, at the same time, may contain linguistic and non-linguistic components. Effective content comprehension can only be achieved by appropriately processing these audio and visual elements. However,this is unfortunately not possible for the full spectrum of consumers without the provision of access services. One of the most closely explored and adopted access services among the traditional audiovisual services is subtitling. Subtitling is not only an essential service for the interpretation of audio information for the deaf and hard-of-hearing (SDH) [2; 3], but has also become a powerful tool for the hearing audience whose barrier is linguistic rather than sensorial (_interlingual_ subtitles) [4]. Furthermore, subtitles can provide benefits in a variety of scenarios and contexts, such as in educational and training environments, in cultural applications, as an assistive tool for (language) learning scenarios and users with cognitive impairments, and in noisy/public environments where the audio cannot (but should be) heard [5]. Therefore, subtitles have not only become a key access service, they are also an intrinsic component of media services. As a result, subtitling is typically considered from a universal perspective, encompassing the two classical categories of subtitles: SDH (mainly _intralingual_, including paralinguistic information, and aimed at persons with hearing loss); and subtitles for hearing users (mainly _interlingual_, but with extra applicability). The current study follows this approach, but focuses the user tests on hearing participants, as a first, but relevant applicability scenario. To date, numerous subtitling solutions for traditional 2D video content have been proposed, even including support for personalization options (e.g., [2; 6; 7]) and advanced presentation methods for better speaker identification (e.g., [8]). In addition, recent studies have begun to explore how accessibility, and subtitling solutions in particular, can be efficiently provided for immersive media services, such as VR360 video. Although the audiovisual content is framed on a flat 2D window in traditional video formats, in VR360 video the users have the freedom to explore omnidirectional 360\({}^{\circ}\) scenes. This has resulted in new challenges and requirements, as analyzed in [9]. Similar to VR360 video, 3D Virtual Reality (VR) content and services are becoming mature and highly popular, not only for entertainment, but also for many other relevant sectors, such as culture [1], communication and collaboration [10], education and training [11], and consultation and therapy [12]. However, accessibility for 3D VR content is still in its infancy. This paper, for the first time, explores two key requirements to address the challenges remaining for efficiently subtitling 3D VR content: presentation modes and guiding methods.