What does Audio Description do when enabled in the iOS Accessibility settings?

Hello. So I was cycling through all of my settings in the accessibility mode for my iPhone. I came across an option called audio description. I turned it on. But I'm not sure how it works.

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#1 Audio Description

Hi there Audio Description is for when you play a movie from iTunes and if there is a Audio Description track available it will play it automatically. Audio Description is called Descriptive Video in the U.S.

#2 Audio discription

The audio discription feature in the accessibility settings allows you to listen to movies and TV shows that are audio described.
That is if the movie or TV shows includes audio discription.
Some apps like Netflix include this feature in there titles.
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