Capture audio and store the last n seconds in a circular buffer.

slice.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include "sndfile.h"
#include "portaudio.h"

#define SAMPLE_RATE 44100
#define FRAMES_PER_BUFFER 1024
#define NUM_SECONDS 3
#define NUM_CHANNELS 2
#define PA_SAMPLE_TYPE paInt16
typedef short SAMPLE;

volatile sig_atomic_t keep_going = 1;

// ring buffer
typedef struct {
    char * buf;
    int size;
} MYDATA;

/*
 * Catch CTRL-C
 */
void catch_sigint(int sig){
    if(sig == SIGINT)
        keep_going = 0;
}

/*
 * Portaudio callback; Keeps last NUM_SECONDS of audio in buffer
 */
static int addNewSamples(const void *inputBuffer, void *outputBuffer,
                           unsigned long framesPerBuffer,
                           const PaStreamCallbackTimeInfo* timeInfo,
                           PaStreamCallbackFlags statusFlags,
                           void *userData) {
    int sizeAdded = framesPerBuffer * NUM_CHANNELS * sizeof(SAMPLE);
    MYDATA * currentData = (MYDATA *)userData;
    int sizeToMove = currentData->size - sizeAdded;
    char * dataToKeep = currentData->buf + sizeAdded;
    char * newData = currentData->buf + sizeToMove;
    char * in = (char *)inputBuffer;

    memmove(currentData->buf,dataToKeep,sizeToMove);
    memmove(newData,in,sizeAdded);

    return 0;
}

/*
 * Interactions
 */
int main(void) {
    PaStreamParameters inputParameters;
    PaStream *stream;
    MYDATA *mydata = malloc(sizeof(MYDATA));
    PaError err;
    const PaDeviceInfo *info;
    int count;
    int i;
    int totalFrames;
    int numSamples;
    int numBytes;

    signal(SIGINT,catch_sigint);

    totalFrames = NUM_SECONDS * SAMPLE_RATE; 
    numSamples = totalFrames * NUM_CHANNELS;

    numBytes = numSamples * sizeof(SAMPLE);

    mydata->buf = (char *)malloc(numBytes);
    mydata->size = numBytes;

    memset(mydata->buf,0,numBytes);

    err = Pa_Initialize();
    if(err != paNoError){
        Pa_Terminate();
        fprintf(stderr, "Error message: %s\n", Pa_GetErrorText(err));
        return -1;
    }

    count = Pa_GetDeviceCount();
    if(count <= 0){
        Pa_Terminate();
        fprintf(stderr, "Error message: No devices!");
        return -1;
    }
    for(i = 0;i<count;i++){
        info = Pa_GetDeviceInfo(i);
        printf("[%d] - %s\n",i,info->name);
    }
    printf("Select an input device: ");
    int dev;
    scanf("%d",&dev);
    if(dev > i - 1 || dev < 0){
        Pa_Terminate();
        fprintf(stderr, "Bad device!\n");
        return -1;
    }

    inputParameters.device = dev;
    inputParameters.channelCount = NUM_CHANNELS;
    inputParameters.sampleFormat = PA_SAMPLE_TYPE;
    inputParameters.suggestedLatency = Pa_GetDeviceInfo(inputParameters.device)->defaultLowInputLatency;
    inputParameters.hostApiSpecificStreamInfo = NULL;

    err = Pa_OpenStream(
              &stream,
              &inputParameters,
              NULL,
              SAMPLE_RATE,
              FRAMES_PER_BUFFER,
              paClipOff,
              addNewSamples,
              mydata);
    if(err != paNoError){
        Pa_Terminate();
        fprintf(stderr, "Error message: %s\n", Pa_GetErrorText(err));
        return -1;
    }

    err = Pa_StartStream( stream );
    if(err != paNoError){
        Pa_Terminate();
        fprintf(stderr, "Error message: %s\n", Pa_GetErrorText(err));
        return -1;
    }

    printf("Now recording");
    fflush(stdout);

    while(keep_going){
        printf(".");
        fflush(stdout);
        sleep(1);
    }

    printf("\n");

    err = Pa_CloseStream( stream );
    if(err != paNoError){
        Pa_Terminate();
        fprintf(stderr, "Error message: %s\n", Pa_GetErrorText(err));
        return -1;
    }

    //Convert to WAV and save to disk when done

    SF_INFO sfinfo;
    SNDFILE * sfd;
    memset (&sfinfo, 0, sizeof (sfinfo)) ;
    sfinfo.samplerate = SAMPLE_RATE;
    sfinfo.channels = NUM_CHANNELS;
    sfinfo.format = (SF_FORMAT_WAV | SF_FORMAT_PCM_16);
    sfd = sf_open("recorded.wav",SFM_WRITE,&sfinfo);
    sf_write_short(sfd,(short *)mydata->buf,numSamples);
    sf_close(sfd);

    Pa_Terminate();
    return 0;
}