Percorrer por autor "Kondoz, A."
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- Reference picture selection using checkerboard pattern for resilient video codingPublication . Carreira, J.; Assunção, P.; Faria, S.; Ekmekcioglu, E.; Kondoz, A.; Lim, H.The improved compression efficiency achieved by the High Efficiency Video Coding (HEVC) standard has the counter-effect of decreasing error resilience in transmission over error-prone channels. To increase the error resilience of HEVC streams, this paper proposes a checkerboard reference picture selection method in order to reduce the prediction mismatch at the decoder in case of frame losses. The proposed approach not only allows to reduce the error propagation at the decoder, but also enhances the quality of reconstructed frames by selectively constraining the choice of reference pictures used for temporal prediction. The underlying approach is to increase the amount of accurate temporal information at the decoder when transmission errors occur, to improve the video quality by using an efficient combination of diverse motion fields. The proposed method compensates for the small loss of coding efficiency at frame loss rates as low as 3%. For a single frame-loss event the proposed method can achieve up to 2 dB of gain in the affected frames and an average quality gain of 0.84 dB for different error prone conditions.
- A robust video encoding scheme to enhance error concealment of intra framesPublication . Carreira, J; Assuncao, P.; Faria. S; Ekmekcioglu, E.; Kondoz, A.In this paper a robust encoding scheme is proposed to improve the visual quality of HEVC decoded video when intra frames are lost along the streaming path. For this purpose, the encoding process includes frame loss simulation and subsequent error concealment, to find the most efficient method that should be used by a decoder to recover lost intra frames. In this novel scheme, each image is divided into partitions, which are associated with the error concealment method that achieves the lowest distortion. Then this information is signalled to the decoder through SEI messages in the coded stream. In order to efficiently use the signalling overhead, rate-distortion optimisation is used to achieve the best trade-off between the number of transmitted symbols and distortion of reconstructed frames. Experimental results show the effectiveness of the proposed method to enhance the quality of reconstructed intra frames under different packet loss ratios (PLR). For PLR=10%, the robust coding scheme is able to improve the average PSNR of all frames affected by errors, up to 1.50 dB and 3.44 dB in Low-Delay and Random-Access configurations respectively, at a maximum overhead cost of 0.24%.
- Selective motion vector redundancies for improved error resilience in HEVCPublication . Carreira, J.; Ekmekcioglu, E; Kondoz, A.; Assuncao, P.; Faria, S.; Silva, V. DeThis paper addresses the problem caused by motion vector coding dependencies on the error resilience performance of the emergent High Efficiency Video Coding (HEVC) standard. We propose a method based on the prediction dependency of motion vectors (MV) to select the most relevant ones for redundant coding with reduced overhead. The spatial dependencies are analysed in the encoder to prioritise the MVs that should be selected for redundancy, based on the number of subsequent dependent coding units. Then, a subset of prioritised MVs is transmitted as redundancy (referred to as side information in the paper), to reduce the use and propagation of mismatched MV predictions in case of transmission errors or data loss. The simulation results show that the proposed MV selection method can effectively identify the most relevant motion field, achieving improved error robustness with a reduced redundancy overhead. Exploiting only 30% of the generated MVs for redundancy, average quality gains of up to 1 dB are achieved compared to a uniform MV selection scheme, and up to 2 dB compared to the original HEVC standard with no redundant encoded information.