In this paper, two new perceptual filters are presented as pre-processing techniques to reduce the bitrate of HEVC compressed Ultra high-definition (UHD) video contents at constant visual quality. The proposed perceptual filters rely on two novel adaptive filters (called BilAWA and TBil) which combine the good properties of the bilateral and Adaptive Weighted Averaging (AWA) filters. Moreover, these adaptive filters are guided by a just-noticeable distortion (JND) model to adaptively control the strength of the filtering process, taking into account the properties of the human visual system. Extensive psychovisual evaluation tests conducted on several UHD-TV sequences are presented in detail. Results show that applying the proposed pre-filters prior to HEVC encoding of UHD video contents lead to bitrate savings up to 23% for the same perceived visual quality.