The following might help if you are having troubles adjusting the volume in movies; music, explosions, gunshots, etc. being too loud or conversations being too quiet.
Navigate to Tools > Preferences.
Select Audio. Check the Normalize volume to: box and set the value to 1.6
Now switch to Advanced view by selecting All in the Show Settings box at the bottom left.
Expand Audio and highlight Filters. Check the Volume Normalizer box. You should see normvol added to the text box at the bottom.
Expand Filters and highlight Volume Normalizer. Set Number of audio buffers to 10 and Maximal volume level to 1.6.
Hit the Save button at the bottom.
Restart VLC, as settings are not applied until restart.