Avaliação de técnicas de redução da resolução espacial de vídeos para dispositivos móveis.

Abstract

This dissertation evaluates the quality of video signals. It is based on subjective and objective evaluation of videos used in digital television for mobile devices. The emergence of digital television implies the need to manipulate videos, in order to adapt them to various devices. Brazil adopted a standard that allocates one band of spectrum for the transmission of television signal for mobile television devices, with a bandwidth of 433 kHz. Because of the bandwidth restriction it is necessary to adjust some parameters such as bit rate and spatial and temporal resolution. Transcoded videos are obtained from the conversion of a video sequence in another with different parameters. This dissertation studies the spatial compression of videos from CIF (352 × 288) to QCIF (176 × 144). To reduce the video a transcoder can be implemented using motion vectors, DCT or fractional interpolator. The fractional interpolator was chosen to be implemented because it has low computational complexity. It employs the average, median, mode and weighted average filters, with windows of 2 × 2, 3 × 3 and 4 × 4. The objective PSNR and SSIM and subjective PC methods, were used to evaluate the quality of the transcoded videos. The subjective evaluation used the H.264 encoder with reduced bit rate and temporal resolution of the video, implemented using a cellular device.