YouTube is introducing machine-generated automatic captioning to YouTube. The captions can also be translated. This obviously has incredible implications for the hearing-impaired and language translation. But it also has great implications for search.
Automatic captions will be generated using Google's automated speech recognition (ASR) technology and the same voice recognition algorithms used in Google Voice.
Additionally, auto-timing is being introduced. If you provide all the words in the video, Google will automatically time the captioning for you.
Of course, having what essentially amounts to transcripts for online video means that the text can be crawled and indexed and then yes - SEARCHED. Bring on the keyword research and seo scriptwriting for online videos!
Google put together a video on how to access the automatic captioning and auto-timing features: