Use a versatile media player like VLC Media Player which can play almost any video codec and handles corrupted or incomplete MP4 files better than default system players.
Digital video recorders often save segments with sequential alphanumeric names. b677.mp4
To give you a better guide, could you tell me or what you expect to see in it (e.g., a specific tutorial, a security recording, or a personal video)? Recommended Video Formats and Settings Use a versatile media player like VLC Media
This filename appears to be a generic system-generated identifier, often used by: a specific tutorial
Use a tool like MediaInfo to see the original "encoded date," the software used to create it, and technical specs (bitrate, resolution).