Judging from OP's comment, they used OpenAI's Whisper speech-to-text transcription model, which was recently released open-source: https://openai.com/blog/whisper/

Ah okay, thank you, I was not aware of this and so I didn't know what to search for. Thanks a lot for the help, much appreciated.

No problem! It's getting harder and harder to keep up with all the stuff getting released in the AI world these days.