YouTube has added closed captioning feature, allowing video producers and uploaders to add captions and subtitles in over 120 languages. This feature also has the potential to allow YouTube to embed ads into videos.
If a video includes captions, viewers can activate them by clicking the caption button located on the bottom right of the video player. Clicking this button will allow viewers to choose which captions they want to see, especially for video with multiple captions. For now caption does not work with embedded YouTube video, you can only access captions when playing videos on YouTube website.
“You can add captions to one of your videos by uploading a closed caption file using the “Captions and Subtitles” menu on the editing page. To add several captions to a video, simply upload multiple files. If you want to include foreign subtitles in multiple languages, upload a separate file for each language.” – The YouTube Team
Some YouTube videos with captioning:
View more information about captioning at YouTube Help Center.