The dashes ( -CM- ) indicate a standardized naming convention: -GroupName- placed before the extension. This tag assures the downloader that the file was not re-encoded by a random user with poor settings. It implies a set of standards: likely crf (constant rate factor) values between 16-18, a preset of "slow" or "veryslow," and probably 10-bit color depth (even for 1080p, to reduce banding).