Subtitles And Closed Captions
The
Videos app includes an Alternate Track button 
,
which you can tap to choose subtitles and captions offered by the
video you're watching. Standard subtitles and captions are usually
listed, but if you prefer special accessible captions, such as
subtitles for the deaf and hard of hearing (SDH), you can set
iPhone to list them instead when they're available.
Prefer accessible subtitles and closed captions for the hard of hearing in the list of available subtitles and captions. Turn on Settings > General > Accessibility > Subtitles & Captioning > Closed Captions + SDH. This also turns on subtitles and captions in the Videos app.
Choose from available subtitles and captions.
Tap 
while
watching a video in Videos.
Customize your subtitles and captions. Go to Settings > General > Accessibility > Subtitles & Captioning > Style, where you can choose an existing caption style or create a new style based on your choice of:
- Font, size, and color
- Background color and opacity
- Text opacity, edge style, and highlight
Not all videos include closed captions.