This thesis aims to create an advanced multimedia player with support of an adaptive stream, securing of the multimedia content and support for playing advertisement. The first part explains the used technologies followed by an analysis of available solutions and the comparison between the two. The theoretical framework is then used to create a player library and a testing application. The player library is based on the framework of ExoPlayer application. Whole application is created in Java for the operation system Android OS.

Streaming 360° video has become more commonplace with content delivery services such as YouTube having support for it. By its nature, 360° video requires more bandwidth as only a fraction of the image is actually in view, while the user is expecting the same "in view" quality as with a regular video. Several studies and lots of work have been done to mitigate this higher demand for bandwidth. One solution is advanced algorithms that take in to account the direction that the user is looking when fetching the video from the server; e.g., by fetching content that is not in the user’s view at a lower quality or by not fetching this data at all. Developing these algorithms is a timely process, especially in the later stages where tweaking one parameter might require the video to be re-encoded, and therefore taking up time that could otherwise be spent on getting results and continued iteration on the algorithm. The viewer should also be considered as the best experience might not correlate with the mathematically best solution calculated by the algorithm. This thesis presents a modular emulator that allows for easy implementation of fetching algorithms that make use of state-of-the-art techniques. It intends to reduce the time it takes to iterate over an algorithm through removing the need to set up a server and encode the video in all of the wanted quality levels when a parameter change would require it. It also makes it easy to include the viewer in the process so that the subjective performance is taken into consideration. The emulator is evaluated through the implementation and evaluation of two algorithms, one serving as a baseline to the second one, which is based on an algorithm developed by another group of researchers. These algorithms are tested on two different types of 360° videos, under four different network conditions and with two values for the maximum buffer size. The results from the evaluation of the two algorithms suggest that the emulator functions as intended from a technical point of view, and as such fulfills its purpose. There is, however, future work that would further prove the emulators performance in regards to replicating real scenarios and a few examples are suggested.

Les interconnections optiques dans les fermes de données (data centers) nécessitent la mise au point de nouvelles approches technologiques pour répondre aux besoins grandissants en composants d’interface respectant des cahiers de charge drastiques en termes de débit, coût, encombrement et dissipation d’énergie. Les peignes de fréquences optiques sont particulièrement adaptés comme nouvelles sources optiques, à mêmes de générer un grand nombre de porteuses optiques cohérentes. Leur utilisation dans des systèmes de transmission en multiplexage de longueurs d’onde (WDM) et exploitant de nouveaux formats de modulation, peut aboutir à des capacités jamais atteintes auparavant. Ce travail de thèse s’inscrit dans le cadre du projet européen BIG PIPES (Broadband Integrated and Green Photonic Interconnects for High-Performance Computing and Enterprise Systems) et a pour but l’étude de peignes de fréquences générés à l’aide de lasers à verrouillage de modes, à section unique, à base de bâtonnets quantiques InAs/InP et puits quantiques InGaAsP/InP. Nous avons entrepris l’étude de nouvelles couches actives et conceptions de cavités lasers en vue de répondre au cahier des charges du projet européen. Une étude systématique du bruit d’amplitude et de phase de ces sources a en particulier été menée à l’aide de nouvelles techniques de mesure afin d’évaluer leur compatibilité dans des systèmes de transmission à très haut débit. Ces peignes de fréquences optiques ont été utilisées avec succès dans des expériences de transmission sur fibre optique avec des débits records dépassant le Tbit/s par puce et une dissipation raisonnable d’énergie par bit, montrant leur fort potentiel pour les applications d’interconnections optiques dans les fermes de données / The increasing demand for high capacity, low cost, high compact and energy efficient optical transceivers for data center interconnects requires new technological solutions. In terms of transmitters, optical frequency combs generating a large number of phase coherent optical carriers are attractive solutions for next generation datacenter interconnects, and along with wavelength division multiplexing and advanced modulation formats can demonstrate unprecedented transmission capacities. In the framework of European project BIG PIPES (Broadband Integrated and Green Photonic Interconnects for High-Performance Computing and Enterprise Systems), this thesis investigates the generation of optical frequency combs using single-section mode-locked lasers based on InAs/InP Quantum-Dash and InGaAsP/InP Quantum-Well semiconductor nanostructures. These novel light sources, based on new active layer structures and cavity designs are extensively analyzed to meet the requirements of the project. Comprehensive investigation of amplitude and phase noise of these optical frequency comb sources is performed with advanced measurement techniques, to evaluate the feasibility of their use in high data rate transmission systems. Record Multi-Terabit per second per chip capacities and reasonably low energy per bit consumption are readily demonstrated, making them well suited for next generation datacenter interconnects

Leon Dash and Ted Conover have modeled an ethnographic approach to literary journalism. This approach combines literary journalism's compelling narrative techniques with ethnographic “naturalist-like” (Brewer, 2000) thoroughness and trustworthiness. Rosa Lee: A Mother in Urban America, by Leon Dash, and Newjack: Guarding Sing Sing, by Ted Conover, exemplify this painstaking method that skillfully uses the narrative craft, generates trustworthy data, and contributes to an academic body of knowledge as well as exposing findings to the general public. Dash, Conover, and others have demonstrated the synergy and problem-solving potential of merging anthropology with literary journalism, yet there is no typology, no common name and no set of ground rules describing this work. Identifying Dash's and Conover's methods may advance cross-pollination between anthropology and literary journalism, fields that share the role of reporting on contemporary culture. This cross-pollination serves both disciplines. Ethnography stands to increase its numbers of readers by enlisting the writing techniques of literary journalists and by publishing “more public-spirited” (Fillmore, 1987, p. 1) findings in more public venues. Literary journalism stands to be seen and applied as a credible form of qualitative science by enlisting trustworthy naturalistic methods and aiming to contribute to an academic body of knowledge. This thesis explores the promise of ethnographic naturalism in narrative form, as “scholarship for real readers” (S. Olsen, March 2, 2009, personal communication) by examining how practitioners meet rigorous naturalistic criteria for trustworthiness (Lincoln & Guba, 1985) and how they present findings in narrative forms and public venues. This exploration draws on personal interviews with Dash and Conover and analyses of their long-form narrative research texts in the context of other scholars' outlooks. Key findings include the discovery that although Dash and Conover were not consciously using naturalistic criteria for trustworthiness, their work meets these criteria. Another key finding is that while both writers consider themselves primarily journalists, they both have read anthropology extensively. A notable finding is the fact that Dash and Conover rely on time-invested “unfettered inquiry,” (Dash, 1996) the mind-set of insatiable curiosity, caring and the liberty to apply practices of other disciplines to conduct research, free from external controls.

Neck pain is the second most common musculoskeletal disorder after low back pain adding to the global burden of disease. A focus on evaluating outcomes for musculoskeletal conditions is imperative to evaluate the effect of interventions and to track the progression of disease. As evidence based practice and associated use of patient-based outcomes are taken up across different countries, it becomes imperative for cross-cultural translation studies. Given the uptake of technology in workplaces, it is also important to understand the prevalence of neck pain in this context. This thesis has focused on two objectives: 1. Translating a newly developed patient-report outcome measure of neck-related disability and testing its psychometric properties. 2. Estimating the prevalence of neck pain in computer-using workers. The first manuscript focusses on cross cultural translation and validation of ND10 (Neck difficulty10) that was designed to measure neck-related disability. A new English outcome measure for neck disability (ND10) was cross culturally translated and validated in computer users in India using forward and backward translation, and cognitive interviewing to determine a final version. The ND10-H demonstrated high reliability (ICC= 0.93) and convergent construct validity with the NDI and DASH (r= 0.78 and 0.86) The second manuscript reported the prevalence of neck pain in computer users in India. Sampling was performed in two different companies: A Spiritual Media Publication Organization (SMPO) and an Information Technology (IT) company. The companies were selected based on computer use and their willingness to participate. The survey was administered to all employees (n=150 & n=54) at these two companies. The overall prevalence of neck pain was 64%. In the IT company, 78% of employees reported neck pain; and in the SMPO the prevalence was 40%. There were no significant differences in prevalence based on gender or age. All of the IT company computer users worked more than seven hours at their computers, while 38% of the SMPO workers did so. Chronic pain was present in 48%of the total sample. The ND10-H can be used to assess neck-related disability in Hindi-speaking individuals. It should be accompanied by a valid pain measure when assessing patient outcomes. The prevalence of neck pain is high in computer-using workers in India. / Thesis / Master of Science Rehabilitation Science (MSc) / 1. Translating a newly developed patient-report outcome measure of neck-related disability and testing its psychometric properties. 2. Estimating the prevalence of neck pain in computer-using workers. The first manuscript focusses on cross cultural translation and validation of ND10 (Neck difficulty10) that was designed to measure neck-related disability. A new English outcome measure for neck disability (ND10) was cross culturally translated and validated in computer users in India using forward and backward translation, and cognitive interviewing to determine a final version. The ND10-H demonstrated high reliability (ICC= 0.93) and convergent construct validity with the NDI and DASH (r= 0.78 and 0.86)

[ES] La distribución de contenidos multimedia, y en particular el streaming de vídeo, domina actualmente el tráfico global de Internet y su importancia será incluso mayor en el futuro. Miles de títulos se agregan mensualmente a los principales proveedores de servicios, como Netflix, YouTube y Amazon. Y de la mano del consumo de contenidos de alta definición que se convierte en la principal tendencia, se puede observar nuevamente un incremento en el consumo de contenidos 3D. Esto ha hecho que las temáticas relacionadas con la producción de contenidos, codificación, transmisión, Calidad de Servicio (QoS) y Calidad de Experiencia (QoE) percibidas por los usuarios de los sistemas de distribución de vídeo 3D sean un tema de investigación con numerosas contribuciones en los últimos años. Esta tesis aborda el problema de la prestación de servicios de transmisión de vídeo 3D bajo condiciones de red de ancho de banda variable. En este sentido, presenta los resultados de la evaluación de la QoE percibida por los usuarios de los sistemas de vídeo 3D, analizando principalmente el impacto de los efectos introducidos en dos de los elementos de la cadena de procesamiento de vídeo 3D: la etapa de codificación y el proceso de transmisión. Para analizar los efectos de la codificación en la calidad del vídeo 3D, en la primera etapa se aborda la evaluación objetiva y subjetiva de la calidad del vídeo, comparando el rendimiento de diferentes estándares y métodos de codificación, con el fin de identificar aquellos que logran la mejor relación entre calidad, tasa de bits y tiempo de codificación. Así mismo, en el contexto de la transmisión en un entorno simulcast, se evalúa la eficacia de la utilización de las codificaciones asimétricas para la transmisión de vídeo 3D, como una alternativa para la reducción del ancho de banda manteniendo la calidad global. En segundo lugar, para el estudio del impacto y el rendimiento del proceso de transmisión, se ha trabajado sobre la base de un sistema de transmisión dinámica adaptativa sobre HTTP (DASH) en el contexto de la transmisión de vídeo tanto 2D como 3D, utilizando diferentes escenarios de variación de ancho de banda. El objetivo ha sido el desarrollo de un marco de referencia para la evaluación de la QoE en escenarios de transmisión adaptativa de vídeo 3D, que permite analizar el impacto en la QoE del usuario frente a diferentes patrones de variación del ancho de banda, así como el rendimiento del algoritmo de adaptación frente a estos escenarios. El trabajo se enfoca en identificar el impacto en la Calidad de Experiencia del usuario que tienen aspectos como: la frecuencia, el tipo, el alcance y la ubicación temporal de los eventos de variación del ancho de banda. El sistema propuesto permite realizar mediciones de rendimiento de forma automatizada y sistemática para la evaluación de los sistemas DASH en el servicio de distribución de vídeo 2D y 3D. Se ha utilizado Puppeteer, la librería Node.js desarrollada por Google, que proporciona una API de alto nivel, para automatizar acciones en el protocolo Chrome Devtools, como iniciar la reproducción, provocar cambios de ancho de banda y guardar los resultados de los procesos de cambio de calidad, marcas de tiempo, paradas, etc. A partir de estos datos, se realiza un procesamiento que permite la reconstrucción del vídeo visualizado, así como la extracción de métricas de calidad y la evaluación de la QoE de los usuarios utilizando la recomendación ITU-T P.1203. / [CA] La distribució de continguts multimèdia, i en particular el streaming de vídeo, domina actualment el trànsit global d'Internet i la seua importància serà fins i tot mes gran en el futur. Milers de títols s'afegeixen mensualment als principals proveïdors de serveis, com ara Netflix, YouTube i Amazon. I de la mà del consum de continguts d'alta definició que es converteix en la tendència principal, es pot observar novament un increment en el consum de continguts 3D. Això ha fet que les temàtiques relacionades amb la producció de continguts, codificació, transmissió, Qualitat de Servei (QoS) i Qualitat d'Experiència (QoE) percebudes pels usuaris dels sistemes de distribució de vídeo 3D siguen un tema de recerca amb nombroses contribucions en els últims anys. Aquesta tesi aborda el problema de la prestació de serveis de transmissió de vídeo 3D sota condicions de xarxa d'ample de banda variable. En aquest sentit, presenta els resultats de l'avaluació de la QoE percebuda pels usuaris dels sistemes de vídeo 3D, analitzant principalment l'impacte dels efectes introduïts en dos dels elements de la cadena de processament de vídeo 3D: l'etapa de codificació i el procés de transmissió. Per analitzar els efectes de la codificació en la qualitat del vídeo 3D, a la primera etapa s'aborda l'avaluació objectiva i subjectiva de la qualitat del vídeo, comparant el rendiment de diferents estàndards i mètodes de codificació, per tal d'identificar aquells que aconsegueixen la millor relació entre qualitat, taxa de bits i temps de codificació. Així mateix, en el context de la transmissió en un entorn simulcast, s'avalua l'eficàcia de la utilització de les codificacions asimètriques per la transmissió de vídeo 3D, com una alternativa per la reducció de l'ampleada de banda mantenint la qualitat global. En segon lloc, per a l'estudi de l'impacte i el rendiment del procés de transmissió, s'ha treballat sobre la base d'un sistema de transmissió dinàmica adaptativa sobre HTTP (DASH) en el context de la transmissió de vídeo tant 2D com 3D, utilitzant diferents escenaris de variació d'ample de banda. L'objectiu ha estat el desenvolupament d'un marc de referència per a l'avaluació de la QoE en escenaris de transmissió adaptativa de vídeo 3D, que permet analitzar l'impacte en la QoE de l'usuari davant de diferents patrons de variació de l'ample de banda; així com el rendiment de l'algorisme d'adaptació davant d'aquests escenaris. El treball s'enfoca a identificar l'impacte a la Qualitat d'Experiència de l'usuari que tenen aspectes com ara: la freqüència, el tipus, l'abast i la ubicació temporal dels esdeveniments de variació de l'ample de banda. El sistema proposat permet realitzar mesuraments de rendiment de manera automatitzada i sistemàtica per a l'avaluació dels sistemes DASH en el servei de distribució de vídeo 2D i 3D. S'ha utilitzat Puppeteer, la llibreria Node.js desenvolupada per Google, que proporciona una API d'alt nivell, per automatitzar accions al protocol Chrome Devtools, com iniciar la reproducció, provocar canvis d'ample de banda i desar els resultats dels processos de canvi de qualitat, marques de temps, parades, etc. A partir d'aquestes dades, es fa un processament que permet la reconstrucció del vídeo visualitzat, així com l'extracció de mètriques de qualitat i l'avaluació de la QoE dels usuaris fent servir la recomanació ITU-T P.1203. / [EN] The distribution of multimedia content, and in particular video streaming, currently dominates global Internet traffic and will become even more important in the future. Thousands of titles are added monthly to major service providers such as Netflix, YouTube and Amazon. In addition to the consumption of high-definition content becoming the main trend, an increase in the consumption of 3D content can be observed again. This fact has caused that issues related to content production, encoding, transmission, Quality of Service (QoS) and Quality of Experience (QoE) perceived by users of 3D video distribution systems became a research topic with numerous contributions in recent years. This thesis addresses the problem of providing 3D video streaming services under variable bandwidth network conditions. In this sense, it presents the results of the evaluation of the QoE perceived by the users of 3D video systems, analyzing mainly the impact of the effects introduced in two of the elements of the 3D video processing chain: the encoding stage and the transmission process. To analyze the effects of the encoding process on the quality of 3D video, the first stage deals with the objective and subjective evaluation of video quality, comparing the performance of different encoding standards and methods, in order to identify those that achieve the best ratio between quality, bit rate and encoding time. Also, in the context of transmission in a simulcast environment, the advantages of using asymmetric coding for 3D video transmission is evaluated as an alternative for bandwidth reduction while maintaining overall quality. Secondly, for the study of the impact and performance of the transmission process, the work has been carried out on the basis of an adaptive dynamic over HTTP (DASH) transmission system in the context of both 2D and 3D video transmission, using different bandwidth variation scenarios. The aim has been to develop a framework for the evaluation of QoE in 3D adaptive video streaming scenarios, which allows analyzing the impact on the user's QoE against different bandwidth variation patterns, as well as the performance of the adaptation algorithm under these scenarios. The work focuses on identifying the impact on the user's Quality of Experience in aspects such as: frequency, type, range and temporal location of bandwidth variation events. The proposed system allows to perform performance measurements in an automated and systematic way for the evaluation of DASH systems in the 2D and 3D video distribution service. The tool Puppeteer, the Node.js library developed by Google, has been used, which provides a high-level API to automate actions in the Chrome Devtools protocol, such as starting playback, causing bandwidth changes and saving the results of the quality change processes, timestamps, stops, etc. From this data, a further processing is performed that allows the reconstruction of the displayed video, as well as the extraction of quality metrics and the evaluation of the QoE of the users using the ITU-T P.1203 recommendation. / Guzmán Castillo, PF. (2022). Evaluación de la QoE en un sistema de streaming adaptativo de vídeo 3D basado en DASH [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/186354 / TESIS

“A Howling in the Paperwork” explores the relationship between ethnography, archival practice, and experimentalism in the work of twentieth century women artists whose syncretic ambitions lead them on a geographical itinerary to and through the greater Caribbean. This dissertation proposes a special synergy between artists with “scattered” bodies of work, in perpetual search of the right form for their creative energy, and the space of the Caribbean with its history of genocides, migrations, and displacements. I focus on women artists, in particular, to foreground the relationship between social precarity and aesthetic innovation. The flight from one technique to another has a push as well as a pull, as women artists have been excluded or expelled from institutional homes for their work, including the university. In the absence of reliable support, the artists I consider come to rely on and refine rigorously subjective methods that prefigure the necessary crisis of objectivity, especially in the social sciences, that would enter mainstream discourse decades later. But even as the artists I consider foreground their own bodies, lives, and communities in their work, they engage diasporic theories of spirit possession, inheritance, and collective creativity that amount to implicit—and sometimes explicit—critiques of the artist as self-contained auteur. Whether or not “there is something strongly feminine” in Caribbean culture, as Antonio Benítez Rojo suggests in The Repeating Island, the idea that there is places women in particularly charged relation to their own creative production in a Caribbean context. My project pays particular attention to the ways these artists attend to one another, taking up the detritus of those who came before as the raw material for new projects. For example, the Cuban-American émigré Ana Mendieta turns to the amateur anthropology of Lydia Cabrera as inspiration for the stone sculptures she carves in the caves of Jaruco, north of Havana, on a return trip to her home island. This relational consciousness does not establish a linear narrative of descent so much as it imagines a transhistorical collaboration in which I, too, participate. Alongside traditional methodologies of close-reading and archival research, I engage their work in more personal ways: I’ve traveled to the caves of Jaruco to visit the almost-ruined remains of Mendieta’s sculptures, I’ve translated Marigloria Palma’s poetry into English, and I’ve interviewed Julie Dash for a literary magazine. Much of the meaning of their work resides in its unmistakable invitation to collaborate in its development and dissemination: the second half of this dissertation considers my own inheritance of feminist practice in the context of Puerto Rican culture.

Les théoriciens de la voix cinématographique, tels Michel Chion, Rick Altman, Mary Ann Doane et Kaja Silverman, évitent une réflexion sur l’expression des rapports de sexe en relation avec l’appartenance raciale ou la question postcoloniale. Au contraire, l’afro-américaine Julie Dash et la vietnamo-américaine Trinh T. Minh-ha se servent de la « caméra-stylo » afin de déconstruire le paradigme dominant de la voix selon lequel l’image serait source de la voix. Les films, Illusions et Daughters of the Dust de Dash, et Reassemblage, Naked Spaces et Surname Viet Given Name Nam de Trinh, désignent l’épistémologie comme un enjeu : les hommes blancs se servent de ce levier que constitue la fabrique de la voix pour investir le lieu du savoir. Ce faisant, ces deux cinéastes contemporaines élaborent un paradigme féministe. La voix masculine transcendante est remplacée par la voix immanente et polyphonique des femmes de couleur. Dash expose les techniques cinématographiques vocales et pratique un montage qui établit une vraisemblance avec la réalité. Nous sommes enveloppés par les voix de ses personnages. Trinh nous fait comprendre « l’architecture » du langage vocal cinématographique et opère un montage qui suspend la continuité. Elle nous incite à en découdre avec des éléments disparates. À travers certains procédés (voix synchronisée/voix désynchronisée par exemple), les femmes portent témoignage de la violence des hommes. Elles révèlent que la justice de la loi du Père est aussi illusoire que la voix cinématographique. D’objet épistémologique, la voix des femmes de couleur devient outil politique : elle détient la promesse de changer les mentalités et de fait, les lois de la cité. / The theoreticians of the cinematic voice, such as Michel Chion, Mary Ann Doane and Kaja Silverman, do not address vocal representation as an issue of gender and its relationship to race and postcolonialism. To the contrary, two contemporary filmmakers, Julie Dash and Trinh T. Minh-ha, use their “caméra-stylo” to deconstruct the dominant paradigm of the voice which has spectators believe that the image is at the source of the voices they hear. The films, Illusions and Daughters of the Dust by Dash, and Reassemblage, Naked Spaces and Surname Viet Given Name Nam by Trinh, show us how the cinematic voice is a construction. The stakes are high: white men use this vocal illusion as a lever to impose control over the world of epistemology. As an alternative, Dash and Trinh propose a feminist paradigm. The transcendent masculine voice is replaced by the immanent and polyphonic voices of women of color. Dash reveals the cinematic techniques of vocal reproduction, and she practices a classical editing that reaches for fidelity. The voices of her characters envelope the spectators. Trinh brings to the screen an understanding of the “architecture” of cinematic language, and her editing techniques suspend continuity. The spectator’s own voice must continually intervene in the construction of meaning. Through various techniques (synchronized/a-synchronized voice), the women characters come forward to witness the violence of men. Their stories reveal that the justice of the Law of the Father is as much an illusion as the cinematic voice. Women of color therefore take up the voice as a political tool: it holds the promise of changing mentalities and, in turn, the laws of city.

[ES] Esta tesis presenta diversas propuestas encaminadas a mejorar la transmisión de vídeo a través del estándar DASH (Dynamic Adaptive Streaming over HTTP). Este trabajo de investigación estudia el protocolo de transmisión DASH y sus características. A la vez, plantea la codificación con calidad constante y bitrate variable como modo de codificación del contenido de vídeo más indicado para la transmisión de contenido bajo demanda mediante el estándar DASH. Derivado de la propuesta de utilización del modo de codificación de calidad constante, cobra mayor importancia el papel que juegan los algoritmos de adaptación en la experiencia de los usuarios al consumir el contenido multimedia. En este sentido, esta tesis presenta un algoritmo de adaptación denominado Look Ahead el cual, sin modificar el estándar, permite utilizar la información de los tamaños de los segmentos de vídeo incluida en los contenedores multimedia para evitar tomar decisiones de adaptación que desemboquen en paradas no deseadas en la reproducción de contenido multimedia. Con el objetivo de evaluar las posibles mejoras del algoritmo de adaptación presentado, se proponen tres modelos de evaluación objetiva de la QoE. Los modelos propuestos permiten predecir de forma sencilla la QoE que tendrían los usuarios de forma objetiva, utilizando parámetros conocidos como el bitrate medio, el PSNR (Peak Signal-to-Noise Ratio) y el valor de VMAF (Video Multimethod Assessment Fusion). Todos ellos aplicados a cada segmento. Finalmente, se estudia el comportamiento de DASH en entornos Wi-Fi con alta densidad de usuarios. En este contexto, se producen un número elevado de paradas en la reproducción por una mala estimación de la tasa de transferencia disponible debida al patrón ON/OFF de descarga de DASH y a la variabilidad del acceso al medio de Wi-Fi. Para paliar esta situación, se propone un servicio de coordinación basado en la tecnología SAND (MPEG's Server and Network Assisted DASH) que proporciona una estimación de la tasa de transferencia basada en la información del estado de los players de los clientes. / [CA] Aquesta tesi presenta diverses propostes encaminades a millorar la transmissió de vídeo a través de l'estàndard DASH (Dynamic Adaptive Streaming over HTTP). Aquest treball de recerca estudia el protocol de transmissió DASH i les seves característiques. Alhora, planteja la codificació amb qualitat constant i bitrate variable com a manera de codificació del contingut de vídeo més indicada per a la transmissió de contingut sota demanda mitjançant l'estàndard DASH. Derivat de la proposta d'utilització de la manera de codificació de qualitat constant, cobra major importància el paper que juguen els algorismes d'adaptació en l'experiència dels usuaris en consumir el contingut. En aquest sentit, aquesta tesi presenta un algoritme d'adaptació denominat Look Ahead el qual, sense modificar l'estàndard, permet utilitzar la informació de les grandàries dels segments de vídeo inclosa en els contenidors multimèdia per a evitar prendre decisions d'adaptació que desemboquin en una parada indesitjada en la reproducció de contingut multimèdia. Amb l'objectiu d'avaluar les possibles millores de l'algoritme d'adaptació presentat, es proposen tres models d'avaluació objectiva de la QoE. Els models proposats permeten predir de manera senzilla la QoE que tindrien els usuaris de manera objectiva, utilitzant paràmetres coneguts com el bitrate mitjà, el PSNR (Peak Signal-to-Noise Ratio) i el valor de VMAF (Video Multimethod Assessment Fusion). Tots ells aplicats a cada segment. Finalment, s'estudia el comportament de DASH en entorns Wi-Fi amb alta densitat d'usuaris. En aquest context es produeixen un nombre elevat de parades en la reproducció per una mala estimació de la taxa de transferència disponible deguda al patró ON/OFF de descàrrega de DASH i a la variabilitat de l'accés al mitjà de Wi-Fi. Per a pal·liar aquesta situació, es proposa un servei de coordinació basat en la tecnologia SAND (MPEG's Server and Network Assisted DASH) que proporciona una estimació de la taxa de transferència basada en la informació de l'estat dels players dels clients. / [EN] This thesis presents several proposals aimed at improving video transmission through the DASH (Dynamic Adaptive Streaming over HTTP) standard. This research work studies the DASH transmission protocol and its characteristics. At the same time, this work proposes the use of encoding with constant quality and variable bitrate as the most suitable video content encoding mode for on-demand content transmission through the DASH standard. Based on the proposal to use the constant quality encoding mode, the role played by adaptation algorithms in the user experience when consuming multimedia content becomes more important. In this sense, this thesis presents an adaptation algorithm called Look Ahead which, without modifying the standard, allows the use of the information on the sizes of the video segments included in the multimedia containers to avoid making adaptation decisions that lead to undesirable stalls during the playback of multimedia content. In order to evaluate the improvements of the presented adaptation algorithm, three models of objective QoE evaluation are proposed. These models allow to predict in a simple way the QoE that users would have in an objective way, using well-known parameters such as the average bitrate, the PSNR (Peak Signal-to-Noise Ratio) and the VMAF (Video Multimethod Assessment Fusion). All of them applied to each segment. Finally, the DASH behavior in Wi-Fi environments with high user density is analyzed. In this context, there could be a high number of stalls in the playback because of a bad estimation of the available transfer rate due to the ON/OFF pattern of DASH download and to the variability of the access to the Wi-Fi environment. To relieve this situation, a coordination service based on SAND (MPEG's Server and Network Assisted DASH) is proposed, which provides an estimation of the transfer rate based on the information of the state of the clients' players. / Belda Ortega, R. (2021). Mejora del streaming de vídeo en DASH con codificación de bitrate variable mediante el algoritmo Look Ahead y mecanismos de coordinación para la reproducción, y propuesta de nuevas métricas para la evaluación de la QoE [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/169467

This thesis reports an experimental characterization of the ultrafast gain and refractive index dynamics of a novel InAs/InGaAsP/InP quantum-dot (QD) semiconductor optical amplifier (SOA) operating near 1.55-µm wavelengths, assessing its high-speed performance characteristics for the first time. The thesis also studies the influence of the degree of quantum confinement on the dynamics of SOAs by comparing the zero-dimensional (0-D) QD's dynamics to those in 1-D InAs/InAlGaAs/InP quantum-dash (QDash), and 2-D InGaAsP/InGaAsP/InP quantum-well (QW) SOAs, both of which also operate near 1.55-µm wavelengths, and are made with matching or similar materials and structures. The ultrafast (around 1 ps) and long-lived (up to 2 ns) amplitude and phase dynamics of the SOAs are characterized via advanced heterodyne pump-probe measurements with 150-femtosecond resolution. It is found that the QD SOA has an 80-picosecond amplitude, and 110-picosecond phase recovery lifetime in the gain regime, 4-6 times faster than the QDash and QW recovery lifetimes, as well as reduced ultrafast transients, giving it the best properties for high-speed (> 100 Gb/s) all-optical signal processing in the important telecommunications wavelength bands. An impulse response model is developed and used to analyze the dynamics, facilitating a comparison of the gain compression factors, time-resolved linewidth enhancement factors (alpha-factors), and instantaneous dynamic coefficients (two-photon absorption and nonlinear refractive-index coefficients) amongst the three structures. The quantum-dot device is found to have the lowest effective alpha-factor, 2-10, compared to 8-16 in the QW, as well as time-resolved alpha-factors lower than in the QW—promising for reduced-phase-transient operation at high bitrates. Significant differences in the alpha-factors of lasers with the same structure are found, due to the differences between gain changes that are induced optically or through the electrical bias. The relative contributions of stimulated transitions and free-carrier absorption to the total carrier heating dynamics in SOAs of varying dimensionality are also reported for the first time. Examining the QD electroluminescence and linear gain spectra in combination with the carrier dynamics also brings about conclusions on the nature of the quantum confinement, dot energy-level structure, and density of states—aspects of the material that have not been previously well understood.