Abstract. Traditionally, the media consumption model has been a passive and isolated activity.However, the advent of media streaming technologies, interactive social applications, and synchronous communications, as well as the convergence between these three developments, point to an evolution towards dynamic shared media experiences. In this new model, geographically distributed groups of consumers, independently of their location and the nature of their enddevices, can be immersed in a common virtual networked environment in which they can share multimedia services, interact and collaborate in real-time within the context of simultaneous media content consumption. In most of these multimedia services and applications, apart from the well-

-Newer social multimedia applications, such as Social TV or networked multi-player games, enable independent groups (or clusters) of users to interact among themselvesand share services within the context of simultaneous media content consumption. In such scenarios, concurrently synchronized playout points must be ensured so as not to degrade the user experience on such interaction. We refer to this process as Inter-Destination Multimedia Synchronization (IDMS). This paper presents the design, implementation and evaluation of an evolved version of an RTCP-based IDMS approach, including an Adaptive Media Playout (AMP) scheme that aims to dynamically and smoothly adjust the playout timing of each one of the geographically distributed consumers in a specific cluster if an allowable asynchrony threshold between their playout states is exceeded. For that purpose, we previously had also to develop a full implementation of RTP/RTCP protocols for NS-2, in which we included the IDMS approach as an optional functionality.Simulation results prove the feasibility of such IDMS and AMP proposals, by adopting several dynamic master reference selection policies, to maintain an overall synchronization status (within allowable limits) in each cluster of participants, while minimizing the occurrence of long-term playout discontinuities (such as skips/pauses) which are subjectively more annoying and less tolerable to users than small variations in the media playout rate.

The combination of broadcast and broadband (hybrid) technologies for delivering TV related media contents can bring fascinating opportunities. It is motivated by the large amount and diversity of media contents, together with the ubiquity and multiple connectivity capabilities of modern consumption devices. This paper presents an end-to-end platform for the preparation, delivery and synchronized consumption of related hybrid (broadcast/broadband) media contents on a single device and/or on multiple close-by devices (i.e., a multi-device scenario). It is compatible with the latest version of the Hybrid Broadcast Broadband TV (HbbTV) standard (version 2.0.1). Additionally, it provides adaptive and efficient solutions for key issues not specified in that standard, but that are necessary to successfully deploy hybrid and multi-device media services. Moreover, apart from MPEG-DASH and HTML5, which are the broadband technologies adopted by HbbTV, the platform also provides support for using HLS and RTP/RTCP broadband technologies. The presented platform can provide support for many hybrid media services. In this paper, in order to evaluate it, the use case of multi-device and multi-view TV service has been selected. The results of both objective and subjective assessments have been very satisfactory, in terms of performance (stability, smooth playout, delays and sync accuracy), usability of the platform, usefulness of its functionalities, and the awaken interest in these kinds of platforms.

The combination of broadcast and broadband (hybrid) technologies for delivering TV related media contents is already a reality. It has been motivated by the large amount and diversity of media contents, together with the ubiquity and multiple connectivity capabilities of modern consumption devices. The use of connected TVs and companion devices (e.g., tablets, smartphones…) is gaining momentum. It enables personalized and enriched TV media experiences, by also exploiting social communication opportunities. Likewise, the media consumption paradigm is worldwide evolving from passive and isolated consumer experiences towards interactive and group shared experiences between remote consumers. Nevertheless, despite the specification of standards, such as Hybrid Broadcast Broadband TV (HbbTV), and the efforts from operators and content providers in the last years, the adoption of hybrid TV media services in Europe is still not as high as expected. This paper presents the concept and some examples of hybrid TV media services, emphasizing the importance of including a combination of media synchronization solutions, known as hybrid sync, to guarantee a satisfactory level of Quality of Experience (QoE). Additionally, it includes the summary and discussion of the results of a research study focused on more than 1000 Spanish users' habits, preferences and expectations regarding four representative hybrid TV media services. Many valuable insights and conclusions have been derived. For instance, the current low market adoption of hybrid TV media services, despite their advantages and the high interest of consumers, and that key technological challenges still need to be overcome. The obtained results and impressions foresee the impact (or potential) of such services in the upcoming TV related media consumption landscape. Therefore, devising proper standard-compliant technological solutions (paying special attention to hybrid sync) and equipment should be continued producing appropriate contents, deploying proper hybrid TV media services and applications. As well, it should be convenient to undertake marketing and commercial efforts to boost their deployment. The contributions of this study can be very valuable to the interested agents to be aware of the remaining challenges, envisage the opportunities, and drive their efforts to maximize the market adoption of such services.

-Currently, several media sharing applications that allow social interactions between distributed groups of users are gaining momentum. This paper focuses on a key factor for providing a satisfying feeling of togetherness in those networked scenarios, which is to ensure synchronous playout between distributed users. This research problem is known as Inter-Destination Media Synchronization (IDMS). Particularly, this paper discusses the benefits of extending RTP/RTCP protocols for IDMS purposes. Accordingly, newly defined RTCP messages and control techniques have been added to a previous version of a centralized RTP/RTCP-based IDMS solution to enable an adaptive, highly accurate and standardized solution.Moreover, as different control schemes for IDMS exist, and each one is best suited for specific use cases, our IDMS solution has been extended to be able to adopt each one of them. Simulation results prove the satisfactory responsiveness of our IDMS solution, as well as its consistent behavior when using each one of the deployed control schemes.

The use of Virtual Reality (VR) technologies and, in particular of VR360 content, can provide great benefits in the society. This particularly applies to the culture and heritage sectors, where venues, goods and events can be digitalized to provide hyper-realistic and engaging experiences, anywhere and anytime. Despite significant advances in the field of VR, there is still an unexplored aspect which is crucial for every service and experience where user interaction is expected: accessibility. This article firstly reviews the needs, challenges and limitations for making VR360 experiences accessible. Based on these facts, an end-to-end platform to efficiently integrate accessibility services within VR360 content is presented. The platform encompasses all steps from media authoring to media consumption, but special attention is given to the accessibility-enabled VR360 player, as it is the end user interaction interface. The presentation modes for the supported access services (like subtitling, audio description and sign language), interaction modalities and personalization features supported by the player are described. To conclude, the availability of newly created and adapted culture-related accessible VR360 content is explored, as a proof of the potential of the contributions work in this sector.

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Inter-Destination Media Synchronization (IDMS) is a key requirement to enable successful networked shared media experiences between remote users. This paper presents an adaptive, accurate and standard-compliant IDMS solution for hybrid broadcast and broadband delivery. Apart from providing multi-and cross-technology support, the presented IDMS solution is able to accomplish synchronization when different formats/versions of the same, or even related, contents are being played out in a shared session. It is also able to independently manage the playout processes of different groups of users. The IDMS solution has been integrated within an end-to-end platform, which is compatible with the Hybrid Broadcast Broadband TV (HbbTV) standard. It has been applied to Digital Video Broadcasting-Terrestrial (DVB-T) technology and tested for a Social TV scenario, by also including an ad-hoc chat tool as an interaction channel. The results of the conducted (objective and subjective) evaluations prove the statisfactory behavior and performance of the IDMS solution and platform as well as in terms of the perceived Quality of Experience (QoE).