Auto-Captioning Video in YouTube

YouTube has provided a way to auto-create caption files from videos you have uploaded. However, the accuracy of the auto-captions is not 100% reliable, especially for disciplinary terms and other specialized language. Therefore, you need to go to the video manager within your YouTube Channel and manually edit the captions. Because of this, it is recommended that you use the auto-caption feature for shorter videos.

To add or edit a captioning file, you must be the owner of the video and have the video uploaded to YouTube.
Automatic captioning works best when the audio is clear and easy to understand. (E.g., background music or speaking in an accent can affect accuracy.)
The automatic captioning option may not be available for all videos.

If you haven’t already, sign in and upload your video to YouTube.

In the top right corner, click on your user profile and select YouTube Studio from the dropdown menu.
This will bring you to your YouTube Studio Channel Dashboard.
Select Subtitles from the menu on the left.
Click on the video you wish to edit subtitles on.
In the Video Subtitles tab and under the field Subtitles, select the pencil icon for Details.

It takes some time for YouTube to process your video; therefore, it may take around 10 minutes or so before the Automatic option shows up.
Test the captions for accuracy by playing the video and reviewing the text concurrently.
To edit the captioning file, select the line that needs repair in the captioning editor text box.
Use the + symbol to add and remove captions as needed.

For additional information about adding captions to your YouTube video, consult the official documentation.

For additional information regarding captioning standards, see 3Play Media's post: The Ultimate Guide to Closed Captioning. For instance, did you know:

99% accuracy is the standard, but always aim for 100%.
Grammar and punctuation matter!
Most captions are between one to three lines of text, are time-synched, and stay on screen for three to seven seconds.