Indicates the file contains two separate "original" (official) audio tracks, typically the original English and the Hindi dub.
The original source of the video was a physical Blu-ray disc, which usually implies high visual fidelity.
This stands for English Subtitles included within the file.
This is the direct sequel to Avengers: Infinity War , where the remaining heroes attempt to reverse the actions of Thanos.
This is an unusual double extension. A .mkv (Matroska) file is a container that supports multiple audio and subtitle tracks, while .mp4 is a more universal format. Seeing both often suggests the file was renamed or modified for specific player compatibility. Context of the Sources