YouTube automatically generates closed captions when you upload a video. Closed captions are the text representation of the words spoken in your video. Captions not only assist those with hearing impairments or no access to audio features, but are also helpful to those that may be less fluent in a specific language to follow along with your video. Captions may be turned on any video by clicking the CC icon in the lower right progress bar of a YouTube video. The captions appear in the lower section of the video.
Example of YouTube icons and text used for closed captioning

It is important to check the accuracy of the captions of your uploaded video. If you find a typo, it is easy to edit and save your corrected caption.

By default, closed captions are turned off YouTube videos. If you would like to open your YouTube video with the closed captions automatically appearing, just add on &cc_load_policy=1 to the end of the address. Here is an example:

Actual embed code used:
<iframe src="" allowfullscreen="allowfullscreen" width="425" height="350"></iframe>

You could also hyperlink closed captions visible like this: