Quality and Behaviour in Immersive Media

As the digital world moves toward more immersive experiences, from 360deg to social Virtual Reality (VR), the request for high-quality, interactive media is growing. Immersive content is inherently data-heavy: a single second of volumetric video can contain millions of points in space, and the VR environment needs to respond in real time to every movement of its user. Delivering these experiences efficiently, without the user noticing the compromises, is one challenge. Understanding how users actually perceive, move through, and interact within these environments is another.

The Distributed and Interactive Systems group addresses both. We study Quality of Experience (QoE), quantifying how compression, streaming and system design affect the perceived quality, but also user behaviour, developing metrics and analytical methods to characterise and understand how people move and interact in VR, in both individual and social settings. The group conducts controlled lab experiments and pilots following mixed methodologies: from in-depth interviews, ethnography to questionnaires, physiological and behavioural signal analysis, the group is equipped with a varied expertises to understand and model the experience of users in immersive media.

Topics

• Quality Evaluation (point clouds and 360-degree video): Delivering high-quality immersive content requires understanding how users perceive it. We evaluate the quality of experience across multiple modalities, combining quantitative and qualitative methods. For point clouds, sets of 3D points representing the surface of humans and objects in virtual immersive systems, we collect subjective scores and user gaza data to assess compression quality and user reliability, while qualitative studies explore users’ perception and uncover quality dimensions needed to build objective metrics. For 360° video, we study the visual distortion characteristics introduced during content production and processing, and their impact on users’ QoE, with the aim of designing perceptually-optimised omnidirectional visual communications;
• Behavioural analysis: Understanding how users behave in virtual environments goes beyond subjective ratings. Thus, we analyse movement trajectories and interaction patterns of users in both single-user and social VR settings, with the aim of developing novel metrics and analytical methodologies to understand. Model and predict user behaviour. This work contributes to a deeper understanding of how people experience and navigate immersive environments, and helps the design of more effective evaluation protocols and immersive systems;
• Social VR evaluation: Social Virtual Reality (Social VR) systems have the potential to support the richness of interactions resembling the face-to-face ones. In this area, we are developing tools and protocols to evaluate such immersive and interactive experiences in Social VR. In particular, we have developed a new evaluation protocol, a new questionnaire and are investigating what objective data to collect for adequate modeling;
• End-to-End latency: Delay is a critical factor in the quality of experience of immersive communication systems. We studied the impact of end-to-end delay on collaborative tasks in Social XR, identifying acceptable thresholds and providing guidelines for designing standardised interaction assessment tasks;
• Multi-party desktop videoconferencing: We investigated how non-system signal, situational, and individual user factors jointly shape the quality of experience in rich media-based conferencing services. This work extended traditional user studies, which normally consist of system factors and subjective ratings, to include user and usage factors.

Funding

• INDUXR
• TRANSMIXR
• MediaScape
• TRACTION
• VRTogether
• REVERIE
• Vconect

Videos

• MMSys2021 - CWIPC-SXR : Point Cloud Dynamic Human Dataset for Social XR - https://www.youtube.com/watch?v=1CctNMseQZ0
• MediaScape XR: https://youtu.be/zzB7B6EAU9c
• MediaScape XR Short: https://youtu.be/I7kY1cMZyD0
• Celebration of CWI’s 75th anniversary in SocialVR: https://youtu.be/KcRpp0s50RQ
• A Social VR Clinic for Knee Arthritis Patients with Haptics: https://youtu.be/c89E98SQRqk
• VRTogether Pilot 3: https://youtu.be/0l82gbTc1WCQ
• VRTogether: Ground-breaking Social Virtual Experiences: https://youtu.be/dL5NX74roBg

Software & Datasets

• Color-based objective quality metric for point cloud contents
• PCM_RR
• PointPCA
• Subjective assessment of dynamic point clouds
• MP3DG: Development framework for point cloud compression algorithms
• VideoLat
• VMC-TB

Publications

• X. Zhou, E. Alexiou, I. Viola, and P. Cesar PointPCA+: A full-reference Point Cloud Quality Assessment Metric with PCA-based Features. Elsevier Signal Processing: Image Communication, , 2025 .
  
  DOI10.1016/j.image.2025.117262 
• X. Zhou, I. Viola, S. Rossi and P. Cesar Comparison of Visual Saliency for Dynamic Point Clouds: Task-free vs. Task-dependent. IEEE Transactions on Visualization and Computer Graphics, , 2025 .
  
  DOI10.1109/TVCG.2025.3549863 
• G. Gautier, X. Zhou, T. Nguyen, J. Jansen, L. Fréneau, M. Viitanen, U. Phan, J. Käpylä, I. Viola, A. Mercat, P. Cesar, and J. Vanne UVG-CWI-DQPC: Dual-Quality Point Cloud Dataset for Volumetric Video Applications. In Proceedings of the ACM International Conference on Multimedia (ACM MM), 2025.
  
  DOI10.1145/3746027.3758263 
• S. Rossi, I. Viola, L. Toni, P. Cesar A Clustering Approach to Unveil User Similarities in 6-DoF Extended Reality Applications. ACM Transactions on Multimedia Computing, Communications and Applications (TOMM), , 2024 .
  
  DOI10.1145/3701734 
• S. Lee, I. Viola, S. Rossi, Z. Guo, I. Reimat, K. Ławicka, A. Striner, P. Cesar Designing and Evaluating a VR Lobby for a Socially Enriching Remote Opera Watching Experience. IEEE Transactions on Visualization and Computer Graphics, , 2024 .
  
  DOI10.1109/TVCG.2024.3372081 
• S. Subramanyam, I. Viola, J. Jansen, E. Alexiou, A. Hanjalic, and P. Cesar Evaluating the Impact of Tiled User-Adaptive Real-Time Point Cloud Streaming on VR Remote Communication. In MM '22: Proceedings of the 30th ACM International Conference on Multimedia, 2022.
  
  DOI10.1145/3503161.3548220 
• J. Gutierrez, P. Perez, M. Orduna, A. Singla, C. Cortes, P. Mazumdar, I. Viola, K. Brunnstrom, F. Battisti, N. Cieplinska, D. Juszka, L. Janowski, M. Leszczuk, A. Adeyemi-Ejeye, Y. Hu, Z. Chen, G. Van Wallendael, P. Lambert, C. Diaz, J. Hedlund, O. Hamsis, S. Fremerey, F. Hofmeyer, A. Raake, P. Cesar, M. Carli, N. Garcia Subjective evaluation of visual quality and simulator sickness of short 360 videos: ITU-T Rec. P.919. IEEE Transactions on Multimedia, , 2021 .
  
  DOI10.1109/TMM.2021.3093717 
• J. Li, S. Subramanyam, J. Jansen, Y. Mei, I. Reimat, K. Ławicka, P. Cesar Evaluating the User Experience of a Photorealistic Social VR Movie. In Proceedings of IEEE International Symposium on Mixed and Augmented Reality (ISMAR 2021), Bari, IT, 2021.
  
  DOI10.1109/ISMAR52148.2021.00044 
• Y. Mei, J. Li, H. de Ridder, P. Cesar CakeVR: A Social Virtual Reality (VR) Tool for Co-designing Cakes. In Proceedings of the SIGCHI Conference on Human Factors in Computing Systems (ACM CHI 2021), Yokohama, JP, 2021.
  
  DOI10.1145/3411764.3445503 
• I. Viola, P. Cesar A reduced reference metric for visual quality evaluation of point cloud contents. IEEE Signal Processing Letters, , 2020 .
  
  DOI10.1109/LSP.2020.3024065 
• I. Viola, S. Subramanyam, and P. Cesar A new Objective Quality Metric for Point Cloud Contents Based on Color. In Proceedings of the International Conference on Quality of Multimedia Experience (QoMEX), Athlone, Ireland, 2020.
  
• S. Subramanyam, J. Li, I. Viola, and P. Cesar Comparing the Quality of Highly Realistic Digital Humans in 3DoF and 6DoF: A Volumetric Video Case Study. In Proceedings of the IEEE Conference on Virtual Reality and 3D User Interfaces (IEEE VR), Atlanta, GA, USA, 2020.
  
  DOI10.1109/VR46266.2020.00031 
• J. Li, Y. Kong, T. Röggla, F. De Simone, S. Ananthanarayan, H. De Ridder, A. El Ali and P. Cesar Measuring and Understanding Photo Sharing Experiences in Social Virtual Reality. In Proceedings of the CHI Conference on Human Factors in Computing Systems Proceedings (CHI 2019), Glasgow, Scotland, UK, 2019.
  
  DOI10.1145/3290605.3300897 
• M. Schmitt, D.C.A. Bulterman, and P. Cesar The Contrast Effect: QoE of Mixed Video-Qualities at the same Time. Springer Quality and User Experience, 3 (1), 2018 .
  
  DOI10.1007/s41233-018-0020-2 
• M. Schmitt, J. Redi, D.C.A. Bulterman, and P. Cesar Towards individual QoE for multi-party video conferencing. IEEE Transactions on Multimedia (TMM), 20 (7): pp. 1781-1795, 2018 .
  
  DOI10.1109/TMM.2017.2777466 
• 2020 IEEE Transactions on Circuits and Systems for Video Technology Best Paper Award
  R. Mekuria, K. Blom, and P. Cesar Design Implementation and Evaluation of a Point Cloud Codec for Tele-Immersive Video. IEEE Transactions on Circuits and Systems for Video Technology, 27 (4): pp. 828-842, 2017 .
  
  DOI10.1109/TCSVT.2016.2543039 
• Jack Jansen and Dick C. A. Bulterman User-centric video delay measurements. In Proceedings of the ACM Workshop on Network and Operating Systems Support for Digital Audio and Video (NOSSDAV 2013), Oslo, Norway, 2013. pp. 37-42.
  
  DOI10.1145/2460782.2460789 
• S. Geerts, I. Vaishnavi, R.N. Mekuria, M.O. van Deventer, and P. Cesar Are We in Sync?: Synchronization Requirements for Watching Online Video Together. In Proceedings of the SIGCHI Conference on Human Factors in Computing Systems (CHI'11), New York, NY, USA, 2011. pp. 311-314.
  
  DOI10.1145/1978942.1978986 

Theses

• Xuemei Zhou, Human-Centric Quality Assessment & Visual Attention Modeling for Point Clouds, TU Delft, The Netherlands. PhD Thesis, 2026.
• Marwin Schmitt, Personal QoE: Accurately Modeling QoE for Multi-Party Desktop Video-Conferencing Based on Systems, Context and User Factors, Vrije Universiteit Amsterdam, The Netherlands. PhD Thesis, 2019.
• Ernestasia Siahaan, Visual Quality of Experience: A Metric Driven Perspective, TU Delft, The Netherlands. PhD Thesis 2018.

Standards

• P.1321 (ex P.IXC) - Interactive test methods for subjective assessment of extended reality communications: https://www.itu.int/itu-t/workprog/wp_item.aspx?isn=20848
• P.919 (ex. P.360-VR) - Subjective test methodologies for 360º video on head-mounted displays: https://www.itu.int/rec/T-REC-P.919/en
• P.1305 (ex P.DTM) - Effect of delays on the tele meeting quality: http://www.itu.int/itu-t/workprog/wp_item.aspx?isn=8897