People with hearing loss may find difficult, or even impossible, to watch a video and understand its content.
For this reason is important to add captions or, if possible, sign language support.
YouTube provides automatic caption support so the person who upload the video doesn't need to create the captions by themselves. However, in situations where the audio is not clear or there is an accent on the language spoken, the automatic captions might have some errors. For this reason, if possible, the user should add captions prior the upload.
The following video shows an example of how captions should be applied:
When adding caption is important to apply the right color contrast rules in order to make the text readible. The most common way is white text on a black background.