: This refers to the audio encoding. DD stands for Dolby Digital, and 5.1 refers to a 5.1 surround sound system, which includes five full-range channels (left, center, right, left surround, right surround) and one low-frequency effects (LFE) channel.
Deep.Impact.1998.1080p.BluRay.x264.DD5.1.mkv deepimpact19981080pbluray1400mbdd51x264 fixed