Since it appears there is a charge to use this API (See the "Resources - Pricing" button), I doubt this api will be very useful to B4x developers because it would then require us to charge our users every time our app uses the API.
I see the original posts from this thread are three years old. Real time speech transcription is a strong interest of mine.
I played with Google's API about a year ago, but at that time they still did not support true real-time recognition, and I was dissuaded by the fee – you have to absorb that, pass it on to the customer, or have the customer create their own account.
I also played with Microsoft's speech API. They also charged a fee.
A problem with true real-time transcription is that you have to continuously send audio to the API or somehow detect start and stop of speech and send only the "busy" portion. Sending continuous speech over the Internet to an API quickly becomes "not real time".
I posted the source, library, and example for something I call CRGoogVR to this forum. You can search for and find it somewhere. It uses the free Android/Google API that's oriented toward non-real-time web searches. I created an app (see the link below in my signature) that uses this library to perform pseudo-real-time recognition.
Google has somewhat recently come out with a free app "Live Transcribe" that does real-time transcription and most likely uses their API. I still like my app better, for several reasons

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Barry.