The feature unveiled Thursday expands upon speech-recognition technology that YouTube began using to make captions available on a limited number of videos late last year.
YouTube's audience will be able to request captions at the press of a button. Video producers will also be able to download the automated captions and improve upon them.
For now, YouTube's captioning tool will only work on videos with English audio, although there are plans to include more languages. The English audio, however, can be translated into 50 different languages.
YouTube, owned by Google, is the Web's most popular video site. Its users upload about 28,800 hours of video each day.