If you can't hear, digital streaming video can be pretty unfriendly. Some technologies don't support closed captions. YouTube does, but having videos professionally captioned is also expensive and time consuming.
Google is rolling out a new feature that will use the voice to text technology of Google Voice to auto caption videos on YouTube. The technology is less than perfect. Sometimes you get garbled results. That's still much better than nothing, and if you've ever watched the close captioning on your TV, you'll notice humans don't always do a better job.
Google is only rolling auto captions out to a few partner sites initially, but they're rolling another feature out to everyone else: auto timing. Previously you had to upload captions to YouTube as SRT files that included text and timing information. Now you just need a text file, and Google will figure out the timing for you. That's a huge time saver.