There is a wide range of video services over complex transmission networks, and in some cases end users fail to receive an acceptable quality level. In this paper, the different factors that degrade users' quality of experience (QoE) in video streaming service that use TCP as transmission protocol are studied. In this specific service, impairment factors are: number of pauses, their duration and temporal location. In order to measure the effect that each temporal segment has in the overall video quality, subjective tests. Because current subjective test methodologies are not adequate to assess video streaming over TCP, some recommendations are provided here. At the application layer, a customized player is used to evaluate the behavior of player buffer, and consequently, the end user QoE. Video subjective test results demonstrate that there is a close correlation between application parameters and subjective scores. Based on this fact, a new metrics named VsQM is defined, which considers the importance of temporal location of pauses to assess the user QoE of video streaming service. A useful application scenario is also presented, in which the metrics proposed herein is used to improve video services 1 .

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There are several subjective test methodologies for assessing video quality, being that each of these methods was developed by considering specific degradation factors in video quality. Therefore, for video streaming services that use TCP as transport protocol different evaluation criteria should be considered as compared to current methods, because the impairment are only pauses. In this paper, the concepts of the mechanisms that integrate perceptual and cognitive processes are studied, relating them to a test environment for subjective evaluation of video, which is limited to streaming video service transmitted via HTTP / TCP. For this reason, some recommendations to perform subjective assessment of streaming video service are proposed, taking into account perceptual and cognitive criteria. In this work, subjective tests are conducted, evaluators with different content preferences assess 3 different video content. Results show that the assessors' QoE depends strongly on video content preferences. Thus, assessors who are interested in the video content are more drastic in the ratings. In the case of sport videos, the Mean Opinion Score (MOS) value of assesors with explicit preference in sports reachs only 54% of the MOS obtained by assessors without interest in sports. Furthermore, the roll of the instructor during the test is also evaluated.

Atualmente existe uma grande variedade de serviços de telecomunicações focados na transmissão de voz, vídeo e dados através de redes complexas, embora, em muitos casos, o usuário final não seja atendido com um nível de qualidade aceitável. Neste trabalho, se avalia como o serviço de streaming de vídeo em uma rede com protocolo Internet (IP) pode ser afetado por uma condição adversa da rede, tal como a variação de atraso (jitter). São mostrados os resultados de avaliações objetivas e subjetivas de streaming de vídeo que indicam que a qualidade de vídeo é diretamente afetada por fatores de degradação da rede IP como a variação de atraso de pacotes. Além disso, se verifica que cenas de maior movimento também são mais afetadas pela variação de atraso. Para a realização dos testes, utiliza-se um cenário de emulação de rede isolado, no qual são parametrizadas diferentes condições de rede. Assim, no canal de transmissão são configurados diversos valores de variação de atraso, obtendo-se uma Base de Dados de vídeos com diferentes graus de degradação de qualidade. Estes vídeos são avaliados utilizando métodos subjetivos: Índice por Categorias Absolutas