The Take.io API from Brazil has a REST protocol with data formats in XML and JSON. According to Take.net, "The take.io RESTful API currently defines five services: SSO, Core, Billing, Messages and Reports." The company states further that, "Take.io is Take.net DNA translated into a set of APIs designed to allow companies to use SMS, MMS, voice, pricing, location, CRM, etc., all of which are integrated with their existing systems."
You can now use the YouTube API to access and create captions for your videos. That means you could let your site visitors refine the transcript to videos you own, or create their own versions of the caption.