Like most of us, Mariella Satow turned to TV and films during lockdown. But her reason for doing so was different. Describing her GCSEs as effectively "cancelled", she wanted to use the extra time on her hands to learn sign language.

She thought she could do this by watching some of her favourite titles online. However she quickly found that while the streamers offered audio in 40 languages none of them provided any sort of sign language.

This led her to spot a gap in the market. Following conversations with the deaf community and money saved up from dog walking, she set paid coders and an interpreter to create what would become Sign Up Captions.

This is a browser extension that allows deaf viewers to experience sign language interpreters in sync with the pictures. She was 17 at the time and not even her parents knew what she was doing until she launched it 2021.

Originally aimed at deaf children in the US who wanted to watch Disney films its grown to 150 films and TV show episodes with 20,000 users a week. Its expanded into the UK and India with Australia next.

But its not always been easy. We get an insight into what its like negotiating with the streaming platforms to try and get them to pay for this. We also find out the mistakes she made in launching a business and getting the right staff.

Now based in California where she is a student, we also found out why subtitles aren't enough, whether she sees AI as a threat and why she thinks accessibility should be serious business rather than simply "a nice thing to do".

Presenter: Peter White

Producer: Julian Paszkiewicz

Listen again on BBC4 - You and Yours Gap Finder