I'm in need for an Android app that allows the user to play back an audio file through the microphone input, so that apps that use voice recognition will hear the audio file I want.
I don't think that will work since most solutions of this type on a PC requires audio-cards (and drivers) that supports this. Sometimes a virtual soundcard is installed to emulate microphone-hardware, but I don't think this is possible on Android, and after a bit of research, app-developers seems to agree. (see link bellow)
http://getjamcast.com/Forum/yaf_postst647_Virtual-Soundcard-for-android.aspx#post3440
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Not an app, but maybe a modified version of the Android OS could be developed to do this?– Nicolas Raoul ♦Feb 17 '18 at 12:58