The segment (or in your keyword, "mmkv" — most likely a common typo for MKV) stands for Matroska Video , an open-standard, free container format. Think of it as a digital box capable of holding video, multiple audio tracks (e.g., Japanese and English), and subtitle tracks all within a single file. The MKV format is highly favored by enthusiasts for its flexibility. A 1080p Blu-ray of Shin Godzilla is typically encoded with the high-quality MPEG-4 AVC or x265 codec and then placed inside an MKV container, preserving the film's original quality. This format is especially popular because it allows you to keep the original Japanese audio, an English dub, and a set of subtitles all in one file, making it an ideal choice for a high-quality personal collection.