get pcm stream while calling

while calling，
1、I want to receive the remote pcm stream byte data， (remote means the opposite voice， not my voice) 。
2、I want to write some pcm byte data ，（just like play a mp3 file  ， send the sound  to the opposite ）

while I read some infomation ， I should use JNI method 。 But it is difficult for me 。 
Could you help me？