In technical communities, "ch1.mp4" is used as a placeholder in code or scripts.
Platforms like Patreon or Google Sites often host chapter-based videos for book read-alouds or software tutorials labeled this way. 3. Programming & Video Scripts
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).