Pipe audio from an input device to another input device using PortAudio. Tested / Built on Mac, should be cross platform. Not the most efficient - working on callback based method.

AudioPipe.cpp

/*
 * AudioPipe.cpp - Alastair Barber 2017.
 * Will open a device, read from it, and write the audio to another device. Eg. Mic -> HDMI sound output
 */

#include "portaudio.h"
#include <iostream>
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>

using namespace std;

#define NUM_CHANNELS 2
#define SAMPLE_RATE (44100)
#define FRAMES_PER_BUFFER (128)

//Not great - put it here so our signal catching method 
// can shut it down when CTRL-C is caught
PaStream *stream;

//Little utility that should try and handle errors
void PA(PaError err, int shouldExit)
{
	if(err == paNoError) return;
	std::cerr << "PortAudio error: " << Pa_GetErrorText(err) << "\n";
	if(shouldExit == 1)
	{
		std::cout << "Shutting down due to error.\n";
		err = Pa_Terminate();
		exit(1);
	}
}

int selectDevice(int showList, string message)
{
	//Assumes PortAudio has been initialised
	if(showList == 1)
	{
		int numDevices;
		int i;
		numDevices = Pa_GetDeviceCount();
		cout << "Found the following devices:\n";
		for(i = 0; i < numDevices; i++)
		{
			cout << "\t" << i << ": " << Pa_GetDeviceInfo(i)->name;
			if(Pa_GetDeviceInfo(i)->maxInputChannels > 0)
			{
				cout << " (Input)";
			}
			if(Pa_GetDeviceInfo(i)->maxOutputChannels > 0)
			{
				cout << " (Output)";
			}
			cout << "\n";
		}
	}
	cout << "Select " << message << " device: ";
	string buffer;
	cin >> buffer;
	return atoi(buffer.c_str());
}

void shutDown()
{
	cout << "Stopping\n";
	PA(Pa_StopStream(stream),0);
	PA(Pa_CloseStream(stream),0);
	Pa_Terminate();
}

void sigHandler(int s)
{
	// std::cout << "\nCaught signal " << s << "\nTerminating\n";
	shutDown();
	exit(0);
}

int main(int argc, char** argv)
{	
	PA(Pa_Initialize(),1);	
	
	// Set up a sigint handler to exit cleanly and terminate port audio
	struct sigaction sigIntHandler;
	sigIntHandler.sa_handler = sigHandler;
	sigemptyset(&sigIntHandler.sa_mask);
	sigIntHandler.sa_flags = 0;
	sigaction(SIGINT, &sigIntHandler, NULL);


	int inputDeviceNumber = selectDevice(1,"Input");
	int outputDeviceNumber = selectDevice(0,"Output");

	PaStreamParameters inParameters;
	PaStreamParameters outParameters;

	bzero(&inParameters, sizeof(inParameters));
	bzero(&outParameters, sizeof(outParameters));


	inParameters.device = inputDeviceNumber;
	inParameters.channelCount = NUM_CHANNELS;
	inParameters.sampleFormat = paFloat32;
	inParameters.hostApiSpecificStreamInfo = NULL;
	inParameters.suggestedLatency = Pa_GetDeviceInfo(inParameters.device)->defaultLowInputLatency;

	outParameters.device = outputDeviceNumber;
	outParameters.channelCount = NUM_CHANNELS;
	outParameters.sampleFormat = paFloat32;
	outParameters.suggestedLatency = Pa_GetDeviceInfo(outParameters.device)->defaultLowOutputLatency;
	outParameters.hostApiSpecificStreamInfo = NULL;

	//Open a stream
	PA(Pa_OpenStream(
			&stream,
			&inParameters,
			&outParameters,
			SAMPLE_RATE,
			FRAMES_PER_BUFFER,
			paClipOff,
			NULL,
			NULL),1);
	
	//Start the stream
	PA(Pa_StartStream(stream),1);
	cout << "Opened - Sending Audio from: " << Pa_GetDeviceInfo(inputDeviceNumber)->name << " to: " << Pa_GetDeviceInfo(outputDeviceNumber)->name <<"\n";
	cout << "CTRL-C to stop\n";
	float sampleBlock[FRAMES_PER_BUFFER * NUM_CHANNELS] = {0};
	while(1)
	{
		PA(Pa_WriteStream(stream, sampleBlock, FRAMES_PER_BUFFER),0);		
		PA(Pa_ReadStream(stream, sampleBlock, FRAMES_PER_BUFFER),0);
	}
	shutDown();
	return 0;
}