Breakpoint Tuning in DCT-Based Nonlinear Layered Video Codecs
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Breakpoint Tuning in DCT-Based Nonlinear Layered Video Codecs Pedro Cuenca Departamento de Inform´atica, Escuela Polit´ecnica Superior de Albacete, Universidad de Castilla-La Mancha, Campus Universitario, 02071 Albacete, Spain Email: [email protected]
Luis Orozco-Barbosa Departamento de Inform´atica, Escuela Polit´ecnica Superior de Albacete, Universidad de Castilla-La Mancha, Campus Universitario, 02071 Albacete, Spain Email: [email protected]
Francisco Delicado Departamento de Inform´atica, Escuela Polit´ecnica Superior de Albacete, Universidad de Castilla-La Mancha, Campus Universitario, 02071 Albacete, Spain Email: [email protected]
Antonio Garrido Departamento de Inform´atica, Escuela Polit´ecnica Superior de Albacete, Universidad de Castilla-La Mancha, Campus Universitario, 02071 Albacete, Spain Email: [email protected] Received 31 August 2003; Revised 2 February 2004 Many studies have been conducted to evaluate the benefits of using layered video coding schemes as a means to improve the robustness of video communications systems. In this paper, we study a frame-aware nonlinear layering scheme for the transport of a DCT-based video over packet-switched networks. This scheme takes into account the relevance of the different elements of the video sequence composing the encoded video sequence. Throughout a detailed study over a large set of video streams, we show that by properly tuning the encoding parameters, it is feasible to gracefully degrade or even maintain the video quality while reducing the amount of data representing the video sequence. We then provide the major guidelines to properly tune up the encoding parameters allowing us to set the basis towards the development of more robust video communications systems. Keywords and phrases: DCT, nonlinear layering video coding, video communications, video quality.
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INTRODUCTION
Recent developments in the areas of video coding and compression techniques are enabling the deployment of computer-based video communications systems. In a video communications system, it is essential to count with a reliable support that is able to guarantee the timely and reliable transport of a video stream. The video process must however incorporate the essential elements to react to potential changes in the service provided by the network. The fact that most video coding schemes use compression techniques makes video communications applications very vulnerable to losses. In the absence of any error control mechanism, the loss of video data causes the loss of information up to the next resynchronization point (e.g., slice head-
ers). In other words, a packet loss will translate in the loss of a partial video slice, where a slice is a full-length row of the image (a whole strip on the screen). This is due to the fact that the slice headers are used as the basic resynchronization points in the video signal. The macroblocks forming a slice contain information coded differentially with respect to precedent macroblocks. More specifically, when a macrobloc
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