Systems like the Meitrack MDVR export files as CH1.mp4 , usually representing the main or front-facing camera.
Knowing the platform (e.g., a forum, a cloud drive, or a security app) will help identify exactly what the file contains.
omarscu - Power System Protection (MCH 416) - 2018-2019 - Google
Professors often post links to recorded sessions using this format, such as "Lec1-ch1.mp4" (Lecture 1, Chapter 1).
Used in Stack Overflow or GitHub examples to demonstrate how to batch-process or play multiple video segments in a loop.
This is a standard way to label the first video in a series of lectures or chapters.