android developpment speech translation

i have a project at school , my mission is to build an android mobile app that will work to translate a real time vocal call conversation for exemple bob who talks with french and alice who talks with english the mission is to translate the speech of bob from french to english and alice speech from english to fench and then sending the translated speech from alice to bob and vice vers ca . so i have decided that i could control the microphone input and output during a call by getting the speech from micro input manipulate it and then send the mipulated speech (for speech manipulation i will work that way :speech to text , use google translate api to translate the text , and then text to speech ) but the problem that i dont know how to control the procces that manges the voice during the call if its possible . idont know wich what are the android os processes that works in background when the call established i have searched in thenet but nothing helps thanks for every advice