OSX Auto Audio Adjuster? On many smart TVs or Windows computers, there is a feature called smart audio adjustment. It basically prevents the audio from going too loud or too quite when playing files that has audio output, such as a movie. I like to know if there is a similar feature or if there is an OSX application that can accomplish similar goal.
That depends what app are you using.

For example iTunes, you can set that up in preferences.



For example VLC player, you can set that up in Audio Effects.



It all depends what app are you using.