The name VTS_01_1.VOB follows a strict hierarchical naming scheme required by DVD players to identify and play content correctly:
Groups related content together. A single DVD can have up to 99 title sets. VTS_01_1.VOB
Contains internal timing data that helps a DVD player jump to specific chapters or handle multi-angle footage. 2. Understanding the Naming Convention The name VTS_01_1
Because VOB files are designed for hardware DVD players, they often require specific software to open on modern computers. A Guide to VOB Files - Adobe VTS_01_1.VOB