A is a lossless rip of a 4K Ultra HD Blu-ray disc. Unlike a standard "rip" or "encode," which compresses the video to save space, a remux takes the original video bitstream and audio tracks directly from the disc and repackages them into a single container—most commonly an MKV (Matroska) file.
It provides the identical 1:1 quality of the original disc without the physical clutter of menus, trailers, or copyright warnings. The Technical Superiority of 4K Remuxes bluray remux 4k
If you see a file labeled Piece: Bluray Remux 4K , here is exactly what you are getting: A is a lossless rip of a 4K Ultra HD Blu-ray disc