One of the top features of the Pixel 4 / 4XL is the Live caption. Today, this feature is enabled on 3rd generation Pixels.
With Live Caption, Pixel 3 owners can instantly enable captions on any videos by clicking on a tab below their on screen phone’s volume slider to instantly add captions. It only works on videos.
This is important for the hearing impaired or non native English speakers where videos are made (e.g. live broadcast) without English subtitles. At the moment it is only available in English with more languages to be supported in the future.