I have speech-to-text working fine from microphone input, but is there some way to feed a speech audio file to the speech recognition plugin?
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As of right now there is no addons that can do that. The best way to do this is to use JavaScript.
with a little internet search this is what I was able to find.
https://stackoverflow.com/questions/46712693/unable-to-covert-audio-to-text-nodejs