To reproduce:
1. Create New Project in older version of Unity editor
2. Add video clip to the project
3. Close editor
4. Open Project in latest Unity version
5. Drag and drop video into the hierarchy
6. Change Audio Output mode to Audio Source
7. Create New Audio Source
8. Assign Audio Source to Video Player
9. Enter Play mode
10. Modify Audio Source parameters

Actual: Audio is not affected by Audio Source parameters changes
Expected: Audio playback should be affected by Audio Source parameters changes

Workaround: Save and reload scene

Reproduced: 2018.2.0a1, 2018.1.0b5, 2017.3.0p3, 2017.1.1p3, 2017.1.0f3
Not Reproducible: 2017.1.0f2

Reproduced on Windows 10 and macOS.