Google-owned YouTube said the latest use of its speech recognition tech is the biggest experiment of its kind online.
YouTube said opening its content to those who could not access it in the past should democratise information to "help foster greater collaboration and understanding".
50 years of speech recognition software
The technology behind speech recognition has been around for about 50 years, said Google engineer Mike Cohen, telling the BBC: "I have been working on speech technology for 25 years."
"There have been steady improvements and this is the culmination of lots of work over years and years. We have had to work on a wide variety of problems like accent variation, background noise, the variation in language, in pronunciation."
Google executive Vic Gundotra, speaking to a recent developers meeting, added: "It is not a complete solution but it is a step on the way to the real solution… It's difficult to get every word exactly right but sometimes that doesn't matter and other times it's amusing."
9 million hard of hearing in UK
Around 9 million people in the UK are deaf or hard of hearing, and Google shows that recent studies predict that over 700 million people worldwide will suffer from hearing impairment by 2015.
"To address a clear need, the broadcast industry began running captions on regular video programming in the early 1970s," Google reminds us over on its blog, noting how generating captions today has to date been a time-consuming and complicated process.
Google released auto-captioning In November of last year for a small, select group of partners, and it is now opening up auto-captions to all YouTube users. Currently, auto-captioning is only for videos where English is spoken.
"Auto-captions aren't perfect and just like any other transcription, the owner of the video needs to check to make sure they're accurate. In other cases, the audio file may not be good enough to generate auto-captions. But please be patient -- our speech recognition technology gets better every day," notes Google.
"For content owners, the power of auto-captioning is significant. With just a few quick clicks your videos can be accessed by a whole new global audience. And captions can make it easier for users to discover content on YouTube."
RNID Director of External Affairs, Emma Harrison, says: "RNID welcomes Google taking this first step towards making YouTube more accessible for deaf and hard of hearing viewers. Captioning will significantly help people with a hearing loss understand video content and increase their ability to share experiences of watching those in which speech plays a prominent part.
"We believe that all on-demand content should be accessible and RNID will continue lobbying hard to ensure that people with a hearing loss have better opportunities to enjoy subtitled videos, movies and television programmes."
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