chrome speech recognition WebKitSpeechRecognition() not accepting input of fake audio device –use-file-for-fake-audio-capture or audio file

I would like to use chrome speech recognition WebKitSpeechRecognition() with the input of an audio file for testing purposes. I could use a virtual microphone but this is really hacky and hard to implement with automation, but when I tested it everything worked fine and the speechrecognition converted my audio file to text. now I wanted to use the following chrome arguments:

--use-file-for-fake-audio-capture="C:/url/to/audio.wav"
--use-fake-device-for-media-stream
--use-fake-ui-for-media-stream

This worked fine on voice recorder sites for example and I could hear the audio file play when I replayed the recording. But for some reason when I try to use this on WebKitSpeechRecognition of chrome then it doesn’t use the fake audio device but instead my actual microphone. Is there any way I can fix this or test my audio files on the website? I am using C# and I couldn’t really find any useful info on automatically adding, managing and configuring virtual audio devices. What approaches could I take?

Thanks in advance.