Quality of experience in skype video calls

Skype is one of the well-known applications that has guided the evolution of real-time video streaming and has become one of the most used software in everyday life. It provides VoIP audio/video calls as well as messaging chat and file transfer. Many versions are available covering all the principal operating systems like Windows, Macintosh and Linux but also mobile systems. Voice quality decreed Skype success since its birth in 2003 and peer-to-peer architecture has allowed worldwide diffusion. After video call introduction in 2006 Skype became a complete solution to communicate between two or more people. As a primarily video conferencing application, Skype assumes certain characteristics of the delivered video to optimize its perceived quality. However in the last years, and with the recent release of SkypeKit1, many new Skype video-enabled devices came out especially in the mobile world. This forced a change to the traditional recording, streaming and receiving settings allowing for a wide range of network and content dynamics. Video calls are not anymore based on static ‘chatting’ but mobile devices have opened new possibilities and can be used in several scenarios. For instance, lecture streaming or one-to-one mobile video conferences exhibit more dynamics as both caller and callee might be on move. Most of these cases are different from “head&shoulder” only content. Therefore, Skype needs to optimize its video streaming engine to cover more video types. Heterogeneous connections require different behaviors and solutions and Skype must face with this variety to maintain a certain quality independently from connection used. Part of the present work will be focused on analyzing Skype behavior depending on video content. Since Skype protocol is proprietary most of the studies so far have tried to characterize its traffic and to reverse engineer its protocol. However, questions related to the behavior of Skype, especially on quality as perceived by users, remain unanswered. We will study Skype video codecs capabilities and video quality assessment. Another motivation of our work is the design of a mechanism that estimates the perceived cost of network conditions on Skype video delivery. To this extent we will try to assess in an objective way the impact of network impairments on the perceived quality of a Skype video call. Traditional video streaming schemes lack the necessary flexibility and adaptivity that Skype tries to achieve at the edge of a network. Our contribution will lye on a testbed and consequent objective video quality analysis that we will carry out on input videos. We will stream raw video files with Skype via an impaired channel and then we will record it at the receiver side to analyze with objective quality of experience metrics.

Il sottotitolaggio per i film festival: due esperienze pratiche

This dissertation aims to examine the field of film festival subtitling by means of the analysis of two subtitling experiences. These experiences will be approached both on a methodological and on a practical level in order to analyse how subtitlers put theory into practice. This approach will also help underline the existing differences in work methodology as far as different work experiences are concerned. The subtitling experiences examined in this dissertation are part of my internships as a subtitler in two Italian film festivals, namely “Umbria Film Festival” and “900 Fest”. In this dissertation, I chose to focus on the subtitling of two of the audiovisual products I translated. These products are a German documentary titled Befreier und Befreite and a Danish fiction film titled Stille Hjerte. This dissertation is divided into five chapters. Chapter 1 describes audiovisual translation at its most theoretical level, focusing on subtitling criteria and strategies. Chapter 2 examines the concept of film translation, focusing on the distinctive features of documentary translation as a specific genre. This chapter also presents the concept of film festival and provides information concerning the translation policies of festivals. Chapter 3 presents the festivals I worked for and details my internship experiences. Chapter 4 focuses on the German documentary and proposes a number of solutions to its main translation problems. Chapter 5 focuses on the Danish film and offers solutions to its translation problems. At the end of the dissertation, I will provide some comments on my internship experiences as well as on the practice of film festival subtitling.