The prefix AgAD is a common characteristic of Telegram's internal file naming convention for media attachments. Because this name is an alphanumeric string generated by a server rather than a descriptive title, the specific content of the video cannot be determined by the filename alone. Technical Profile
Do you have on where this file was found or what you expect the video to be? AgADkwgAAmRUiFY.mkv
This is a Matroska Video container. It is a flexible, open-standard format that can hold unlimited tracks of video, audio, picture, or subtitle tracks in one file. The prefix AgAD is a common characteristic of