By default, the volume slider in VLC allows you to increase the volume up to 125%. If you have a file with really low, inaudible audio, you may want to boost the volume above 125%.
Increasing audio volume above 100% percent causes audio distortion; it may harm your audio equipment; it might even cause pain in your ear. So you need to be very careful when increasing the volume above 100%, especially if you are using a Headphone.
Increasing volume up to 200% using the Keyboard
Using the keyboard shortcut, the volume can be increased up to 200% without having to change any VLC setting. The shortcut to increase volume is CTRL+UP To decrease volume use CTRL+DOWN
Changing the volume slider maximum
As mentioned before, the maximum volume which can be achieved using the volume slider is 125%, by default. This default setting can be changed from preferences.
From the tools menu choose preferences or press CTRL+P. Make sure that show all settings is selected.
This would change the preferences window from Simple preferences to Advanced preferences. Go to Interface ➾ Main interfaces ➾ Qt ➾ Maximum volume displayed.
Set the maximum volume displayed to the desired percentage.