Google has created a feature that allows videos to have captions. To be able to add captions to a video you will need to create either a caption file or a transcript file. A caption file contains two important types of information, one is the text that will be displayed in the video and the other is the information regarding the time when a specific text should be displayed in the video. A transcript file only contains text, and if the caption is in English, Google provides the option of using speech algorithms to add the captions to the video in the corresponding time it needs to be displayed.
There is software available that can create these files for you, such as MovCaptioner, Overstream or Subtitle Workshop. There is also the option of captioning yourself, but you have to keep in mind that there are different types of information which needs to be displayed such as narration, dialogue and sound effects. The files that are currently compatible with YouTube are SubView and SubRip, so make sure you obtain those types of files if you hire someone to create them for you or purchase any software.
After you create your transcript or caption file, you will need to log in to your YouTube account and add them to their corresponding video. YouTube provides a captions button that will allow you to add your file, all you need to do is select the type of file and browse for it.
This new feature for YouTube creates a new opportunity for SEO; it will allow videos to be ranked, since the keyword in the captions will be index by search engines. Pages that have video will have a lot more text compared to a page that has video without captions, and this will allow a better rank on a search. It may also create a lot of traffic to sites such as YouTube, since they will appear more on search results.