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Imperceptibility requirement in video watermarking is more challenging compared with its image counterpart due to the additional dimension existing in video. The embedding system should not only yield spatially invisible watermarks for each frame of the video, but it should also take the temporal dimension into account in order to avoid any flicker distortion between frames. While some of the methods in the literature approach this problem by only allowing arbitrarily small modifications within frames in different transform domains, some others simply use implicit spatial properties of the human visual system (HVS), such as luminance masking, spatial masking, and contrast masking. In addition, some approaches exploit explicitly the spatial thresholds of HVS to determine the location and strength of the watermark. However, none of the former approaches have focused on guaranteeing temporal invisibility and achieving maximum watermark strength along the temporal direction. In this paper, temporal dimension is exploited for video watermarking by means of utilizing temporal sensitivity of the HVS. The proposed method utilizes the temporal contrast thresholds of HVS to determine the maximum strength of watermark, which still gives imperceptible distortion after watermark insertion. Compared with some recognized methods in the literature, the proposed method avoids the typical visual degradations in the watermarked video, while still giving much better robustness against common video distortions, such as additive Gaussian noise, video coding, frame rate conversions, and temporal shifts, in terms of bit error rate.