Look back at the chat or folder where you found it; often the message accompanying the file provides the context (e.g., a movie title, a recorded meeting, or a personal clip).

Files named this way are usually generated when someone uploads a video to a cloud service or messaging app. How to identify the content:

The .mkv extension (Matroska Video) indicates this is a high-quality video file that can hold multiple tracks (audio, subtitles, etc.).

If you have this file and want to know what it is without playing it, you can try the following:

In systems like Telegram, "AgAD..." is a common prefix for unique identifiers assigned to media files (photos, videos, or documents) stored on their servers. Because this is a machine-generated ID rather than a descriptive title, there isn't a "public record" or standard text describing its contents. What this file likely contains:

Use a tool like MediaInfo to see the internal title, encoding date, or tags that might be hidden inside the file.