Simple Duplex

Demonstrates duplex mode which is where data is captured from a microphone and then output to a speaker device.

This example captures audio from the default microphone and then outputs it straight to the default playback device without any kind of modification. If you wanted to, you could also apply filters and effects to the input stream before outputting to the playback device.

Note that the microphone and playback device must run in lockstep. Any kind of timing deviation will result in audible glitching which the backend may not be able to recover from. For this reason, miniaudio forces you to use the same sample rate for both capture and playback. If internally the native sample rates differ, miniaudio will perform the sample rate conversion for you automatically.

#include "../miniaudio.h"

#include <stdio.h>

#ifdef __EMSCRIPTEN__
void main_loop__em()

void data_callback(ma_device* pDevice, void* pOutput, const void* pInput, ma_uint32 frameCount)
    MA_ASSERT(pDevice->capture.format == pDevice->playback.format);
    MA_ASSERT(pDevice->capture.channels == pDevice->playback.channels);

    /* In this example the format and channel count are the same for both input and output which means we can just memcpy(). */
    MA_COPY_MEMORY(pOutput, pInput, frameCount * ma_get_bytes_per_frame(pDevice->capture.format, pDevice->capture.channels));

int main(int argc, char** argv)
    ma_result result;
    ma_device_config deviceConfig;
    ma_device device;

    deviceConfig = ma_device_config_init(ma_device_type_duplex);
    deviceConfig.capture.pDeviceID  = NULL;
    deviceConfig.capture.format     = ma_format_s16;
    deviceConfig.capture.channels   = 2;
    deviceConfig.capture.shareMode  = ma_share_mode_shared;
    deviceConfig.playback.pDeviceID = NULL;
    deviceConfig.playback.format    = ma_format_s16;
    deviceConfig.playback.channels  = 2;
    deviceConfig.dataCallback       = data_callback;
    result = ma_device_init(NULL, &deviceConfig, &device);
    if (result != MA_SUCCESS) {
        return result;

#ifdef __EMSCRIPTEN__


#ifdef __EMSCRIPTEN__
    emscripten_set_main_loop(main_loop__em, 0, 1);
    printf("Press Enter to quit...\n");


    return 0;
Copyright © 2021 David Reid
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