I've been searching around the subject for a while, and haven't found any substantial track yet.
My aim is to build a Speech-to-Text converter that would be used to generate and display live captions on the fly on a tv, the exact way Youtube close-captioning works.
I know that I would likely have to embed the code on a powerful board, like a Raspberry Pi, and I also know that Google has released its Automatic Speech Recognition API so it could potentially be used so as to handle the speech-to-text conversion part of the project.
However, the part that still seems rather unclear is how the input sound will be redirected from the tv to the processing component (the Pi for example), and how the Pi will be able to display the output generated captions on the tv ?
PS: As the matter might be tagged as too broad, I want to clarify that I'm not asking for a in-depth/detailed answer or a step-by-step method to carry it out, but rather some guidelines and basic advices as to which direction should be followed, which technology is most suitable, etc ...