Web-based Platform for Subtitles Customization and Synchronization in Multi-Screen Scenarios

This paper presents a web-based platform that enables the customization and synchronization of subtitles on both single- and multi-screen scenarios. The platform enables the dynamic customization of the subtitles' format (font family, size, color...) and position according to the users' preferences and/or needs. Likewise, it allows configuring the number of subtitles lines to be presented, being able to restore the video playout position by clicking on a specific one. It also allows the simultaneous selection of various subtitle languages, and applying a delay offset to the presentation of subtitles. All these functionalities can also be available on (personal) companion devices, allowing the presentation of subtitles in a synchronized manner with the ones on the main screen and their individual customization. With all these functionalities, the platform enables personalized and immersive media consumption experiences, contributing to a better language learning, social integration and an improved Quality of Experience (QoE) in both domestic and multi-culture environments.


INTRODUCTION
Subtitles play a key role in TV and online video services. For many users, such as those with audiovisual impairments or non-natives, subtitles are essential to access and interpret audiovisual contents. Likewise, multimedia services and applications need to be adaptive regarding the users' needs, preferences and resources. With these premises in mind, this paper presents a web-based platform that enables the customization and synchronization (sync, hereafter) of subtitles on both single-and multi-screen scenarios. The platform allows dynamically adapting and customizing the subtitles' presentation according to the users' needs (e.g., language), sensorial capabilities (e.g., format and size), preferences (e.g., format, size, location, number of lines…), the type (e.g., smartphone, tablet, TV…) and number of available devices, the application dynamics and the context of the targeted environment (e.g., domestic or public places…), while guaranteeing a synchronized playout.
During the demo session, the audience will be able to experiment with the platform, by interacting with it on main screens and using their own companion devices to create new, or join ongoing, multi-screen sessions. We also expect valuable feedback about its performance, design aspects, applicability, usability and future functionalities.

PLATFORM FOR SUBTITLES CUSTOMIZATION & SYNC
The technological components that have been used to develop the presented platform and its main functionalities are briefly described in this section.

Technological Components
The platform has been developed by exclusively using webbased components, such as HTML5, CSS3 and JavaScript (e.g., Node.js, Socket.IO, jQuery…), which allows guaranteeing universal (i.e., cross-network, cross-device, cross-platform and cross-browser) support. More details about these components and the advantages of web platforms compared to native platforms can be found in [4].

Functionalities
The platform is mainly comprised of an initial screen for selecting the (Youtube or HTML5) video or playlist, and the initial language (see Figure 1) and a main (player) screen with the subtitles controls (see Figures 2 to 4). In particular, the main screen includes controls for: 1) enabling and disabling the subtitles; 2) selecting their language; 3) simultaneously selecting various languages; 4) selecting the number of lines to be displayed (e.g., the previous and next ones); and 5) customizing the subtitles format (font family, size, color, background color and contrast). It is also possible to set a (positive or negative) delay offset to the presentation of subtitles and restoring the video playout position to the beginning of a specific subtitle line by clicking on it. In full screen mode (Figure 3), it is possible to modify the position of subtitles (subtitles vs surtitles) and to apply a transparency percentage to them. Interestingly, the platform allows showing a QR for the association of companion devices by scanning it. This way, the subtitles can be presented in a synchronized and Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for third-party components of this work must be honored. For all other uses, contact the Owner/Author.  (Figure 4) in multi-screen scenarios. Remote playback control can also be enabled. The advantages of our platform compared to other existing ones are summarized in Table 1 (+ means  better performance or extra functionalities).
The platform has been objectively and subjectively evaluated, having obtained very satisfactory results in terms of performance, usability, usefulness of its functionalities, its applicability and the awaken interest. Demo videos showing many of its capabilities are available at: http://iim.webs.upv.es/prototypes.html#streaming

FUTURE WORK
As future work, we plan to make our platform compatible with the Hybrid Broadcast Broadband TV (HbbTV) standard and to adopt artificial intelligence techniques, such as voice synthesis/recognition and image recognition.

ACKNOWLEDGMENTS
This work has been funded, partially, by the "Fondo Europeo de Desarrollo Regional (FEDER)" and the Spanish Ministry of Economy and Competitiveness, under its R&D&I Support Program, in project with Ref.