Broadcasters could be forced soon to offer closed captions for any TV show they're streaming online and previously aired on TV, if U.S. Senate passes a new bill that calls for it. 

Video bloggers and smaller online studios won't have to start transcribing each and every show. 

Experts believe that broadcasters actually have a lot to gain using closed captions:

• It provides a means of access for some 36 million deaf or hearing-impaired Americans. 
• Transcripts make web video searchable, making them a natural SEO tool.
• Researchs show that video with captions are viewed 38 percent longer than videos without

There are many video platforms (Brightcove, Ooyala, Kit Digital, Amigot Interactive...) that include captioning this service. YouTube automatically transcribe videos.

Here it is worth noting that there is an interesting project called The Universal Subtitles project that crowdsource the transcription of web videos.