Immersive Virtual Reality (VR) and Volumetric Video (VV) technologies enable highly realistic and interactive experiences but impose significant computational and bandwidth demands. This paper presents a comprehensive end-to-end architecture, along associated technological components and workflows specifically designed to support these advanced services and experiences on lightweight devices like smartphones and even standalone VR headsets via Remote Rendering. By offloading demanding processing tasks to a Remote Renderer, the proposed architecture is able to interactively provide low-latency rendered streams from complex VR scenes including live VV feeds (e.g., holoported users), enabling seamless participation via browser-based thin clients. The proposed framework includes the exploration of advanced stereoscopic delivery strategies, supporting viewport-aware projections to concentrate visual quality within the user’s Field of View (FoV) while enabling seamless exploration with reduced bandwidth overhead. Furthermore, it incorporates 6 Degrees of Freedom (6DoF) capabilities and diverse interaction features from the thin clients. Preliminary evaluations demonstrate promising latency outcomes, achieving end-to-end latency levels under 40ms in local scenarios and motion-to-photon latency levels around 180 ms over the Internet, as well as system stability regardless of VR scene complexity. Ultimately, this work proposes a robust foundation for democratizing premium VR experiences, actively supporting versatile one-to-many delivery scenarios.

Video door entry systems installed at scale in residential buildings predominantly rely on unshielded twisted-pair wiring, whose useful bandwidth is limited to a few hundred kHz—a constraint to provide video transmission. Replacing this infrastructure or resorting to high-cost xDSL/PLC modems is economically prohibitive for the vast majority of deployments.

When a theater is demolished, the performances, the acoustics, and the shared experience of attending disappear with the building. Virtual Reality can bring these elements back inside a reconstructed space, provided the reconstruction goes beyond static visualization. This work presents an integrated framework to enable shared, interactive and immersive visits to lost theatrical heritage, combining visual and acoustic reconstruction, a catalog of theatrical performances with subtitles, Points of Interest with multilingual audio narration, and real-time volumetric capture of remote visitors rendered as holographic presences inside the virtual space. The approach is demonstrated through Casa de Comedias de l’Olivera, a Valencian theater first built in 1584, rebuilt in 1618, and demolished in the mid eighteenth century.

Directing a live presentation involves continuous decision-making: selecting which camera feed or scene to display, synchronizing visual content with the speaker’s narrative, and responding to the presenter’s actions in real time. In many settings where presentations occur (classrooms, seminars, webinars, videoconferences), this process is either absent or handled manually by the presenter or a dedicated operator. This paper explores whether multimodal AI techniques, executed locally on consumer hardware, can support the automation of this process. It presents a proof of concept for a system referred to as an AI director: a modular pipeline built with open-source components that processes a live video feed alongside audio transcription and gesture recognition to describe the presenter’s actions and extract information from the presentation content. All processing runs on-device, with no cloud dependency. The system is part of a broader work in progress toward multi-camera automated direction; the paper reports on the devised architecture, the selected components, and preliminary observations on feasibility and resource constraints.

The increasing miniaturization of Unmanned Aerial Vehicles (UAVs) has expanded their deployment potential to indoor and hard-to-reach areas. However, this trend introduces distinct challenges, particularly in terms of flight dynamics and power consumption, which limit the UAVs’ autonomy and mission capabilities. This paper presents a novel approach to overcoming these limitations by integrating Neural 3D Reconstruction (N3DR) with small UAV systems for fine-grained 3-Dimensional (3D) digital reconstruction of small static objects. Specifically, we design, implement, and evaluate an N3DR-based pipeline that leverages advanced models, i.e., Instant-ngp, Nerfacto, and Splatfacto, to improve the quality of 3D reconstructions using images of the object captured by a fleet of small UAVs. We assess the performance of the considered models using various imagery and pointcloud metrics, comparing them against the baseline Structure from Motion (SfM) algorithm. The experimental results demonstrate that the N3DR-enhanced pipeline significantly improves reconstruction quality, making it feasible for small UAVs to support high-precision 3D mapping and anomaly detection in constrained environments. In more general terms, our results highlight the potential of N3DR in advancing the capabilities of miniaturized UAV systems.

Volumetric video compression is essential for addressing processing and bandwidth challenges, while minimizing perceptual quality loss, in emerging holographic tele-transportation (i.e. holo-portation) services. Research in this field has primarily focused on compression efficiency and/or on real-time performance, but less attention has been given to the perceptual impact of volumetric video compression when viewing dynamic sequences of human holograms at varying distances in Virtual Reality (VR) scenarios. This paper first provides objective evidence on the promising performance of a novel Video-based Point Cloud Compression Codec (V*-PCC) compared to a state-of-the-art Geometry / anchor octree-based (G-PCC) codec. Then, the V*-PCC codec is adopted to run a user study in which observers view sequences of volumetric holographic user representations at different compression levels, shown at varying distances. The results reveal two key insights: (i) perceptual quality improves at equivalent compression settings as the viewing distance increases; and (ii) compression artifacts become less noticeable and more tolerable at greater distances. These findings not only support the need for further Quality of Experience (QoE) studies but interestingly reinforce the potential of devising dynamic viewport- and position-aware encoding strategies to overcome current scalability and interoperability limitations in this field.

This paper presents a research framework for investigating Quality of Experience (QoE) aspects when interactively exploring reconstructions of cultural heritage in Virtual Reality (VR) settings. In particular, it revolves around a reconstruction of the Corral de Comèdies de l’Olivera, a 16th-century theater from Valencia demolished in 1748. The presented framework enables an interactive exploration of the reconstructed virtual environment through various navigation methods and User Interface (UI) presentation approaches, specifically designed for VR. Likewise, the reconstruction includes diverse Points of Interest (PoIs) containing historical information, theatrical performances including diverse video formats, and a personalized presentation of accessibility features. Overall, the paper aims to showcase how immersive technologies can preserve and disseminate cultural heritage that no longer exists physically. The modular implementation of the considered interaction features and methods additionally constitute a powerful framework to explore and validate QoE design patterns for optimal virtual heritage experiences.

Social eXtended Reality (XR) is poised to become a dominant medium for remote communication, social interaction, and collaboration in the near future.However, its potential can be significantly magnified by integrating additional technological enablers.On the one hand, the support for realistic and volumetric holographic representations of users, captured in real-time via affordable setups, will result in enhanced levels of quality of interaction, co-presence and trustworthiness compared to using synthetic avatar-based user representation formats.On the other hand, the availability of highquality multi-modal virtual production tools will enrich the immersion, interaction and storytelling possibilities, while it will allow providing such engaging services to large-scale audiences via 2D video distribution platforms.This paper presents a strategic vision toward achieving a modular and seamless integration between innovative Social XR, holographic communication, and virtual production tools to exploit all such potential advantages.In particular, it proposes a high-level architectural framework to cohesively integrate such technological enablers, accommodating novel features to meet newly derived requirements.Then, it outlines potential applicability scenarios and reports preliminary results as initial evidence of the full achievable potential.

Next-generation networks have become key enablers for distributed eXtended Reality (XR) services, which pose stringent demands in terms of bandwidth, compute and reliability. In this context, the Network as a Service (NaaS) paradigm, where the network offers APIs tailored to specific vertical domains, is a promising approach to enhance delivery protocols and communications for XR services. In this paper, we present NetXRate which is a new NaaS API tailored to interactive XR services. NetXRate leverages Open RAN (O-RAN) and the network exposure capabilities of the 5GCore, to deliver rate recommendations to XR applications based on the instantaneous capacity available in the cellular network. Using a simulative approach, we demonstrate how NetXRate can be integrated with two state-of-the-art Over-the-Top (OTT) XR rate recommendation strategies, achieving a reduction of up to 72% in outage probability in scenarios with severe network congestion where multiple XR users compete for higher share of bandwidth in the same cell.

This paper elaborates on a set of research objectives to optimize multi-user Social Virtual Reality (VR) experiences. A first objective consists of designing and developing a novel and lightweight Volumetric Video (VV) pipeline to provide 3D realistic user representations (i.e., holograms), increasing the visual resolution and real-time performance compared to state-of-the-art solutions. A second objective consists of designing and implementing novel modular communication architectures, integrating virtualized in-cloud media processing functions with the goal of enhancing the scalability and interoperability in Social VR. A third objective consists of designing and implementing a set of multimodal Human Computer Interaction (HCI) features to be integrated in Social VR experiences to enable rich group-based interaction and effective collaboration. All such envisioned contributions will be thoroughly (objectively and subjectively) evaluated in relevant use cases, like culture and tourism, to validate their benefits and shed some light on associated hypotheses.

Scalability, interoperability, and cost efficiency are key remaining challenges to successfully providing real-time holo-portation (and Metaverse-like) services. This paper, for the first time, presents the design and integration of a Multipoint Control Unit (MCU) in a pioneering real-time holo-portation platform, supporting realistic and volumetric user representations (i.e., 3D holograms), with the aim of overcoming such challenges. The feasibility and implications of adopting such an MCU, in comparison with state-of-the-art architectural approaches, are assessed through experimentation in two different deployment setups, by iteratively increasing the number of concurrent users in shared sessions. The obtained results are promising, as it is empirically proved that the newly adopted stream multiplexing together with the novel per-client and per-frame Volumetric Video (VV) processing optimization features provided by the MCU allow increasing the number of concurrent users, while: (i) significantly reducing resources consumption metrics (e.g., CPU, GPU, bandwidth) and frame rate degradation on the client side; and (ii) keeping the end-to-end latency within acceptable limits.

Traditional tools used to evaluate the Quality of Experience (QoE) of users after browsing an ad, using a product, or performing any kind of task typically involves surveys, user testing, and analytics. However, these methods provide limited insights and have limitations due to the need of users’ active cooperation and sincerity, the long testing time, the high cost, and the limited scalability. On this work we present the tools we are developing to automatically evaluate QoE in different use cases such as dashboards that show on real time reactions to different events in the form of emotions and affections predicted by different models based on physiological data. To develop these tools, we require datasets on affective computing. We highlight some limitations of the available ones, the difficulties during the creation of such data, and our current work in the confection of a new one with automatic annotation of ground truth.

This paper contains the research proposal of Juan Antonio De Rus presented at the IMX 23 Doctoral Symposium. Virtual Reality (VR) applications are already used to support diverse tasks such as online meetings, education, or training, and the usages grow every year. To enrich the experience VR scenarios, include multimodal content (video, audio, text, synthetic content) and multi-sensory stimuli are typically included. Tools to evaluate the Quality of Experience (QoE) of such scenarios are needed. Traditional tools used to evaluate the QoE of users performing any kind of task typically involves surveys, user testing or analytics. However, these methods provide limited insights for our tasks with VR and have shortcomings and a limited scalability. In this doctoral study we have formulated a set of open research questions and objectives on which we plan to generate contributions and knowledge in the field of Affective Computing (AC) and Multimodal Interactive Virtual Environments. Hence, in this paper we present a set of tools we are developing to automatically evaluate QoE in different use cases. They include dashboards to monitor in real time reactions to different events in the form of emotions and affections predicted by different models based on physiological data, as well as the creation of a dataset for AC and its associated methodology.

This paper reports on the research being done towards enabling and understanding interactive social VR360 video viewing scenarios, by exclusively relying on web-based technologies, and using different types of consumption devices. After motivating the relevance of the research topic and associated impact, the paper elaborates on key requirements, features, and system components to effectively enable such scenarios, such as: adaptive and low-latency streaming, media synchronization, social presence, interaction channels, and assistive methods. For each of these features and components, different alternatives are assessed and proof of concept implementations are being provided. With an effective combination and integration of all these contributions, an end-to-end platform can be built and used as a research framework to explore the applicability and potential benefits of social VR360viewing in a variety of use cases, like education, culture or surveillance, by tailoring the technological components based on lessons learned from experimental studies. These use case studies can also provide relevant insights into activity patterns, behaviors, and preferences in Social Viewing scenarios.

The production and consumption of multimedia content is continuously increasing, and this particularly affects to immersive formats, like VR360 video. Even though significant advances have been witnessed with regard to the processing, delivery and consumption of interactive VR360 video, key challenges and research questions still need to be addressed to efficiently provide interactive multi-camera and multi-user VR360 video services over distributed and heterogeneous environments. This research work aims at providing novel and efficient contributions to overcome existing limitations in this topic. First, it will develop an end-to-end modular web-based VR360 video platform, including the measurement of Quality of Service (QoS) and activity metrics, to be used as a research testbed. Second, it will provide lightweight yet efficient viewport-aware video processing and delivery strategies to dynamically concentrate the video resolution on the user’s viewport, with a single stream and decoding process through the web browser. Third, it will propose innovative encoding, signaling and synchronization solutions to enable an effective support for multi-camera and multi-device VR360 services, in a synchronized manner and with the lowest latency possible. Fourth, it will explore how to effectively provide social viewing scenarios between remote users while watching the same or related VR360 videos, assisted with interactive and guiding techniques.

This paper contains the research proposal of Miguel Fernández Dasí that was presented at the MMSys 2022 doctoral symposium.1 The production and consumption of multimedia content is continuously increasing, and this particularly affects to immersive formats, like VR360 video. Even though significant advances have been witnessed with regard to the processing, delivery and consumption of interactive VR360 video, key challenges and research questions still need to be addressed to efficiently provide multi-camera and multi-user VR360 video services over distributed and heterogeneous environments. This research work aims at providing novel and efficient contributions to overcome existing limitations in this topic. First, it will develop an end-to-end modular VR360 video platform, including the measurement of Quality of Service (QoS) and activity metrics, to be used as a research testbed. Second, it will provide web-compliant viewport-aware video processing and delivery strategies to dynamically concentrate the video resolution on the users' viewport, with a single stream and decoding process through the web browser. Third, it will propose innovative encoding, signaling and synchronization solutions to enable an effective support for multi-camera VR360 services, with personalized, fast and in-sync switching features. Fourth, it will explore how to effectively provide social viewing scenarios between remote users while watching the same or related VR360 videos. The work also plans to contribute with low-latency delivery pipelines as well as with tools and algorithms to assess and model the Quality of Experience (QoE).

Abstract Accessibility is a key requirement for any multimedia tool and application. With the current trend towards immersive experiences, such as Virtual Reality (VR) and 360o video, it becomes key that these environments are adapted to be fully accessible. However, until recently the focus has been mostly on adapting the existing techniques to fit immersive displays, rather than considering new approaches for accessibility designed specifically for these increasingly relevant media experiences. This paper surveys a wide range of 360o video players and examines the features they include for dealing with accessibility, such as Subtitles, Audio Description, Sign Language, User Interfaces and other interaction features, like voice control and support for multi-screen scenarios. These features have been chosen based on guidelines from standardization contributions, like in the World Wide Web Consortium (W3C) and the International Communication Union (ITU), and from research contributions for making 360° video consumption experiences accessible. The in-depth analysis has been part of a research effort towards the development of a fully inclusive and accessible 360° video player. The paper concludes by discussing how the newly developed player has gone above and beyond the existing solutions and guidelines, by providing accessibility features that meet the expectations for a widely used immersive medium, like 360° video.

When designing and deploying multimedia systems, it is essential to accurately know about the necessary requirements and the Quality of Service (QoS) offered to the customers. This paper presents two open-source software tools that contribute to these key needs. The first tool is able to measure and register resources consumption metrics for any Windows program (i.e. process id), like the CPU, GPU and RAM usage. Unlike the Task Manager, which requires manual visual inspection for just a subset of these metrics, the developed tool runs on top of the Powershell to periodically measure these metrics, calculate statistics, and register them in log files. The second tool is able to measure QoS metrics from DASH streaming sessions by running on top of TShark, if a non-secure HTTP connection is used. For each DASH chunk, the tool registers: the round-trip time from request to download, the number of TCP segments and bytes, the effective bandwidth, the selected DASH representation, and the associated parameters in the MPD (e.g., resolution, bitrate). It also registers the MPD and the total amount of downloaded frames and bytes. The advantage of this second tool is that these metrics can be registered regardless of the player used, even from a device connected to the same network than the DASH player.

Software Defined Wireless Networks offer an opportunity to enhance the performance of specific services by applying centralized mechanisms which make use of a global view of the network resources. This paper presents FALCON, a novel solution that jointly optimizes fair airtime allocation and rate recommendations for Server and Network Assisted DASH video streaming, providing proportional fairness among the clients. Since this problem is NP-hard, FALCON introduces a novel heuristic algorithm that is proved to achieve almost optimal results in a practical amount of time. The performance of FALCON is evaluated when used in conjunction with three referent Adaptive Bit Rate strategies (PANDA, BOLA and RobustMPC) in a simulated ultra-dense In-flight Entertainment System scenario. The obtained results show that FALCON provides significant benefits by minimizing instability and buffer underruns, while obtaining a fair video rate and airtime allocation among clients, thus contributing to an enhanced Quality of Experience.

This paper introduces the Point Cloud Multipoint Control Unit (PC-MCU): a key component for multi-user holoconferencing systems, where remote participants are represented as Point Clouds. The presented solution redefines the idea of MCU, broadly used to optimize connections and communications between users in traditional videoconferencing, and introduces a set of key features for the optimization of holoconferencing services where multiple users can be remotely connected. The PC-MCU is a virtualized cloud-based component, that aims at reducing the end-user client computational resources and bandwidth usage, providing the following key features: fusion of volumetric videos, Level of Detail (LoD) adjustment and non visible data removal. The results obtained for a scenario with two remote users, show how the introduction of the PC-MCU provides significant benefits in terms of computational resources and bandwidth savings, thus alleviating the requirements at the client side in holoconferencing services when compared to a baseline condition without using it. These improvements open the door to further research on this area to enable scalable and adaptive holoconferencing services using lightweight devices.

This paper reports on the work being done towards achieving an immersive and accessible reconstruction of Historical and Cultural Heritage, focusing on Theaters of the Early Modern as use case. In particular, the paper presents and discusses potential possibilities to enable: 1) the acoustical reconstruction of the virtual (lost) environments – beyond the graphical reconstruction for the buildings, elements and performances; 2) effective interaction features and navigation within the virtual environment (e.g. by means of adaptive interfaces, guiding methods, insertion of Point of Interest); and 3) accessible experiences, by means of an innovative and personalized presentation modes for access services, like subtitles and audio description. For most of these aspects and features, proof of concept implementation are provided, and opportunities for future work are outlined. With an effective combination of all these contributions, the goal is to bring back valuable (both tangible and intangible) Cultural Heritage from the past, providing high benefits in relevant sectors like Culture, Tourism and Education.

ImmersiaTV is a H2020 European project that targets the creation of novel forms of TV content production, delivery and consumption to enable customizable and immersive multi-screen TV experiences. The goal is not only to provide an efficient support for multi-screen scenarios, but also to achieve a seamless integration between the traditional TV content formats and consumption devices with the emerging omnidirectional ones, thus opening the door to new fascinating scenarios. This paper initially provides an overview of the end-to-end platform that is being developed in the project. Then, the created contents and considered pilot scenarios are briefly described. Finally, the paper provides details about the consumption part of the ImmersiaTV platform to be showcased. In particular, it enables a customizable, interactive and synchronized consumption of traditional and omnidirectional contents from an opera performance, in multiscreen scenarios, composed of main TVs, tablets and Head Mounted Displays (HMDs).

The encoding, delivery and interactive consumption of omnidirectional videos still face many challenges. Traditional encoding techniques, based on Equirectangular Projection (ERP) formats, introduce significant pixel redundancy. This has prompted the appearance of advanced solutions based on the segmentation in separate regions or tiles, and their selective delivery depending on the users' viewpoint. However, tiling techniques introduce further challenges. First, neighboring pixels are encoded separately, which may result in noticeable separations between regions. Second, they can involve synchronization problems when the users' viewpoints change. Third, they may require further extensions to existing technologies, such as Dynamic Adaptive Streaming over HTTP (DASH), which makes their adoption in current web browsers very challenging. The use of Cubemap Projection (CMP) is alternatively gaining popularity due to its advantages compared to ERP. However, it requires the streaming of the whole 360° area. This paper proposes a novel tiled Cubemap (TiCMP) strategy that overcomes all the mentioned limitations. TiCMP is based on dividing the cube into two tiles, adaptively streaming them based on the users' viewpoint, and playing them out in a synchronized manner in web-based players. Evaluation results demonstrate that TiCMP provides significant bandwidth savings, without negatively impacting the Quality of Experience (QoE) when compared to traditional Equirectangular- and Cubemap-based strategies.

This paper presents an end-to-end Dynamic Adaptive Streaming over HTTP (DASH) platform, developed by using open-source components. It includes and allows the configuration of all the required steps along the end-to-end media delivery chain, from the encoding, segmentation and storage of the media content at the server side, to the delivery and adaptive consumption of the media content at the client side. A key component of this platform is the DASH client, developed using the GStreamer framework. It includes a module with a novel adaptive algorithm for switching between the available representations (i.e., qualities) of the media content at the server side, based on the available bandwidth and on internal conditions and features of the client (such as the buffer occupancy level, the battery level, its charging state and the CPU load). It also includes different modules to simulate specific values for these parameters, and to visualize their values and the value of the selected quality in real-time. A preliminary evaluation has proved the satisfactory performance of the overall platform. Finally, links to demo videos are provided to demonstrate the satisfactory performance and capabilities of this platform.

Inter-Destination Multimedia Synchronization(IDMS) is a key requirement to enable satisfying group shared media experiences. This paper presents the design and simulation of a Distributed Control Scheme (DCS) for IDMS. In this scheme, geographically dispersed receivers exchange(multicast) RTCP reports on their arrival and play out timing for RTP packets, and each one of them uses the collected reports from the other receivers belonging to the same logical group (or cluster) to adaptively adjust its local play out timing such that an overall synchronization status (within allowable limits) is maintained. Also, the strengths (interactivity, flexibility, scalability, and robustness) and weaknesses (traffic overhead, security) of a DCS for IDMS are discussed, in comparison with centralized approaches. Moreover, a simple technique to enhance the performance in terms of coherence when using the DCS for IDMS is proposed. Simulation results prove the effectiveness of the proposed control scheme and techniques to guarantee concurrently synchronized play outpoints for independent clusters of receivers.

Inter-Destination Media Synchronization (IDMS) is essential for enabling pleasant shared media experiences. The goal of my PhD thesis is to design, develop and evaluate an advanced RTP/RTCP-based IDMS solution fitting the requirements of the emerging distributed media consumption paradigm. In particular, standard compliant extensions to RTCP are being specified to allow for an accurate, adaptive and dynamic IDMS control when using RTP for streaming media. Moreover, the feasibility and suitability of several architectural schemes for exchanging the IDMS information, algorithms for allowing a dynamic IDMS monitoring and control, as well as adjustment techniques are being investigated. Objective and subjective testing are being conducted to validate the satisfactory performance of our IDMS solution and to provide insights about the users' tolerance on asynchrony levels in different IDMS scenarios.

Inter-Destination Media Synchronization (IDMS) is essential in the emerging media consumption paradigm, which is radically evolving from passive and isolated services towards dynamic and interactive group shared experiences. This paper concentrates on improving a standardized RTP/RTCP-based solution for IDMS. In particular, novel Early Event-Driven (EED) RTCP feedback reporting mechanisms are designed to overcome latency issues and to enable higher flexibility, dynamism and accuracy when using RTP/RTCP for IDMS. The faster reaction on dynamic situations (e.g., detection of asynchrony or channel change delays) and a finer granularity for synchronizing media-related events, while preserving the RTCP bandwidth bounds, are validated through simulation tests.

Many emerging multimedia applications enable independent groups (or clusters) of consumers to interact between them and share services within the context of simultaneous media content consumption. Owing to the semantic, spatial or temporal dependency among the involved media streams, concurrently synchronized playout points must be ensured so as not to spoil the user experience on such interaction. This paper presents the combination of an evolved Inter-Destination Multimedia Synchronization (IDMS) approach and a new designed Adaptive Media Playout (AMP) scheme that aims to smoothly adjust the playout timing of each one of the receivers in a specific cluster, if an asynchrony threshold between their playout states is exceeded. Simulation results prove the feasibility of such proposals, by employing several dynamic master selection policies, to maintain an overall synchronization status (within allowable limits) in each cluster, while minimizing the occurrence of long-term playout discontinuities (such as skips/pauses) which are subjectively more annoying to users than small variations in the media playout rate.

This paper presents an enhanced version of a proposed extension of the RTP/RTCP standard protocols to acquire Inter-Destination Multimedia Synchronization (IDMS) in one-way distributed applications. Several dynamic policies for selecting the master reference play out point to synchronize are introduced and their suitability is analyzed, for specific network conditions and application requirements, according to the impact of the play out adjustments (such as skips and/or pauses) on the overall quality and the buffer fullness variation. Simulation results prove the ability of our approach, for all the proposed master selection algorithms, to maintain the play out asynchrony between distributed receivers within acceptable limits, by dynamically adjusting their play out timing every time an allowed play out time discrepancy between their play out states is detected.

This paper presents an accurate simulation framework for video streaming evaluation. We have designed a full RTP/RTCP implementation for NS-2 and we propose to combine it with several multimedia tools to obtain an RTP-based tool-set that allows the measurement of network-level QoS and most common video quality metrics. As RTCP feedback reporting capabilities have been provided, researchers and practitioners could make us of this platform to assess novel source and receiver-based techniques for improving the QoS in multimedia streaming services.

Nowadays, many multimedia cluster-to-cluster applications exist, such as 3D tele-immersion (3DTI), computer-supported collaborative workspaces (CSCWs), distributed multimedia presentations (DMP).... All these applications have sophisticated data transport requirements due to the use of multiple, semantically related flows of information. A synchronization mechanism must be used to synchronize the playout of the streams, regardless of the number of receivers and the number of streams played on the receiver clusters. In this paper, we present a new solution for multimedia group synchronization in such applications. Rather than base the solution on the definition of a new synchronization protocol (as other authors do), we base it on small modifications or extensions to RTP/RTCP standard protocols already used in most multimedia applications. Due to this, the overload introduced by the approach is minimal. The suitability of the approach was evaluated in a real one-way cluster-to-cluster application, with satisfactory results.