Need to play audio to the caller

For my app I need to play a pre recorded message to the caller. Say if someone calls my phone and I enable the app it should play back the audio such that the caller hears it. I tr开发者_如何转开发ied setting the stream STREAM_DTMF,STREAM_VOICE_CALL ... (tried all of them) but nothing worked. STREAM_MUSIC made the audio play through the speaker but was not such that the caller could hear it ...

Tried searching around but have not found any answer yet ... would really appreciate if someone can respond !

This is not directly possible on current android phones, as the outgoing call audio does not pass through the application processor on which linux and android run.