Using the SDL microphone with libopus in loopback

gistfile1.txt

#include <SDL2/SDL.h>
#include <opus.h>
#include <opus_types.h>
#include <stdlib.h>

static SDL_Window *window = NULL;
static SDL_Renderer *renderer = NULL;
static SDL_AudioSpec spec;
static SDL_AudioDeviceID devid_in = 0;
static SDL_AudioDeviceID devid_out = 0;

int sampling_rate = 48000;
int channels = 1;
int frameSize = 480;

OpusEncoder* encoder;
OpusDecoder* decoder;
unsigned char encoded[1024 * 16];

static void loop()
{
    SDL_bool please_quit = SDL_FALSE;
    SDL_Event e;

    while (SDL_PollEvent(&e)) {
        if (e.type == SDL_QUIT) {
            please_quit = SDL_TRUE;
        } else if (e.type == SDL_KEYDOWN) {
            if (e.key.keysym.sym == SDLK_ESCAPE) {
                please_quit = SDL_TRUE;
            }
        } else if (e.type == SDL_MOUSEBUTTONDOWN) {
            if (e.button.button == 1) {
                SDL_PauseAudioDevice(devid_out, SDL_TRUE);
                SDL_PauseAudioDevice(devid_in, SDL_FALSE);
            }
        } else if (e.type == SDL_MOUSEBUTTONUP) {
            if (e.button.button == 1) {
                SDL_PauseAudioDevice(devid_in, SDL_TRUE);
                SDL_PauseAudioDevice(devid_out, SDL_FALSE);
            }
        }
    }

    if (SDL_GetAudioDeviceStatus(devid_in) == SDL_AUDIO_PLAYING) {
        SDL_SetRenderDrawColor(renderer, 0, 255, 0, 255);
    } else {
        SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);
    }
    SDL_RenderClear(renderer);
    SDL_RenderPresent(renderer);

    if (please_quit) {
        /* stop playing back, quit. */
        SDL_Log("Shutting down.\n");
        SDL_PauseAudioDevice(devid_in, 1);
        SDL_CloseAudioDevice(devid_in);
        SDL_PauseAudioDevice(devid_out, 1);
        SDL_CloseAudioDevice(devid_out);
        SDL_DestroyRenderer(renderer);
        SDL_DestroyWindow(window);
        SDL_Quit();
        exit(0);
    }

    /* Note that it would be easier to just have a one-line function that
        calls SDL_QueueAudio() as a capture device callback, but we're
        trying to test the API, so we use SDL_DequeueAudio() here. */
    while (SDL_TRUE) {
        Uint8 buf[frameSize * sizeof(float) * channels];

        float *samples = (float *)&buf;

        const Uint32 br = SDL_DequeueAudio(devid_in, buf, sizeof (buf));

        // Amplify!
        for (int i = 0; i < frameSize * channels; i++) {
            samples[i] *= 32;
        }

        int encodedSize = opus_encode_float(encoder, samples, frameSize, (unsigned char *) &encoded, sizeof(encoded));
        printf("Encoded size: %d (%f%%)\n", encodedSize, 100.0 / sizeof(buf) * encodedSize);

        Uint8 decodedBuf[1024 * 16];
        float *decodedSamples = (float *)&decodedBuf;

        int decodedSize = opus_decode_float(decoder, (unsigned char *) &encoded, encodedSize, decodedSamples, frameSize, 0);
        // printf("Decoded size: %d %d\n", decodedSize, decodedBuf[8]);

        SDL_QueueAudio(devid_out, decodedBuf, br);

        if (br < sizeof (buf)) {
            break;
        }
    }
}

int
main(int argc, char **argv)
{
    int application = OPUS_APPLICATION_AUDIO;
    int err;

    // Create opus
    encoder = opus_encoder_create(sampling_rate, channels, application, &err);

    if (err) {
        printf("Err creating encoder %d", err);
        exit(-1);
    }

    decoder = opus_decoder_create(sampling_rate, channels, &err);

    if (err) {
        printf("Err creating decoder %d", err);
        exit(-1);
    }

    //encoded = (unsigned char *)calloc(1024 * 16 * 4);

    /* (argv[1] == NULL means "open default device.") */
    const char *devname = argv[1];
    SDL_AudioSpec wanted;
    int devcount;
    int i;

    /* Enable standard application logging */
    SDL_LogSetPriority(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_INFO);

    /* Load the SDL library */
    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO) < 0) {
        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't initialize SDL: %s\n", SDL_GetError());
        return (1);
    }

    window = SDL_CreateWindow("testaudiocapture", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 320, 240, 0);
    renderer = SDL_CreateRenderer(window, -1, 0);
    SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
    SDL_RenderClear(renderer);
    SDL_RenderPresent(renderer);

    SDL_Log("Using audico driver: %s\n", SDL_GetCurrentAudioDriver());

    devcount = SDL_GetNumAudioDevices(SDL_TRUE);
    for (i = 0; i < devcount; i++) {
        SDL_Log(" Capture device #%d: '%s'\n", i, SDL_GetAudioDeviceName(i, SDL_TRUE));
    }

    SDL_zero(wanted);
    wanted.freq = sampling_rate;
    wanted.format = AUDIO_F32SYS;
    wanted.channels = channels;
    wanted.samples = 4096;
    wanted.callback = NULL;

    SDL_zero(spec);

    /* DirectSound can fail in some instances if you open the same hardware
       for both capture and output and didn't open the output end first,
       according to the docs, so if you're doing something like this, always
       open your capture devices second in case you land in those bizarre
       circumstances. */

    SDL_Log("Opening default playback device...\n");
    devid_out = SDL_OpenAudioDevice(NULL, SDL_FALSE, &wanted, &spec, SDL_AUDIO_ALLOW_ANY_CHANGE);
    if (!devid_out) {
        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't open an audio device for playback: %s!\n", SDL_GetError());
        SDL_Quit();
        exit(1);
    }

    SDL_Log("Opening capture device %s%s%s...\n",
            devname ? "'" : "",
            devname ? devname : "[[default]]",
            devname ? "'" : "");

    devid_in = SDL_OpenAudioDevice(argv[1], SDL_TRUE, &spec, &spec, 0);
    if (!devid_in) {
        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't open an audio device for capture: %s!\n", SDL_GetError());
        SDL_Quit();
        exit(1);
    }

    SDL_Log("Ready! Hold down mouse or finger to record!\n");

    while (1) { loop(); SDL_Delay(16); }

    return 0;
}