: The video compression codec used (also known as AVC). It is highly compatible with almost all modern media players, smart TVs, and computers.
: The vertical resolution of the video (1920 x 1080 pixels), which is standard Full High Definition. Watchmen.2009.Ultimate.Cut.1080p.BluRay.H264.AA...
: This is likely the beginning of the "release group" tag (e.g., AMIABLE, ARCHiViST), which identifies the community or individual responsible for creating and uploading that specific digital copy. : The video compression codec used (also known as AVC)
: The movie title and its original theatrical release year. Watchmen.2009.Ultimate.Cut.1080p.BluRay.H264.AA...
That string is a standard file naming convention used by digital media release groups to identify a specific version of a movie.