YouTube has been working hard to expand the offerings at the site and make the videos more accessible to everyone. One of the features they just recently rolled out was the ability to include captions in videos.
When uploading a video to YouTube now you also have the option to upload a closed caption file for the video. You can even include multiple languages my adding multiple files. This could really get your message out to the masses. It would not only allow your video's content to be heard but also seen by those with hearing disabilities or lack of audio hardware (like some office computers).
The supported formats for captions are Subviewer and Subrip (*.sub/ *.srt). In order to upload a captions file, visit your account's video edit page (accessible via Account -> My Videos) and switch to the "Captions and Subtitles" entry on top. Although Youtube is missing a web-based captions editor tool, they do recommend a few software programs and tools for creating subtitle/caption file formats, including URUSoft's Subtitle Workshop which also supports the aforementioned formats as well as many others and over 35 languages.
Plus with the addition of multiple language files you could reach a new non-English speaking audience as well. YouTube currently supports over 120 languages which should cover just about everyone on the planet.
When you have uploaded the files, viewers will be able to activate the captions through the video player menu (by clicking on the up arrow icon in the lower right hand side of the video. Users can then choose which language they would like to see the captions in. I would embed the video so that you could see it in action but apparently Youtube is not supporting this feature in the embed yet.
Not only will this allow for greater accessibility, but it will give YouTube excellent data for searching videos and targeting advertising to them. If you think about it, a complete set of subtitles for captions is basically the same as a transcript of the video itself, and we know how transcripts can help with video indexing.
Major YouTube partners including BBC Worldwide, CNET and MIT have already embraced the new technology. It does mean you will need to take extra time to get captions created for your videos and you might need to find a translator if you wanted to do multiple languages, but the potential benefits are innumerable and that extra time could turn into a variety of things including traffic to your site, conversions and new business.
So if you're using YouTube as a part of your marketing campaign and planting viral videos then you should definitely think about adding captions to the videos to get a higher level of awareness for your brand, products and message.