Record into WAV file

Question

Since I've posted this question, I've been trying to write a valid WAV file myself from raw PCM data. I've managed to write the FLAC converter (tested and works), but it does not encode the WAV files I've been writing.

I'm not sure what I'm doing wrong. I've been scouring the internet looking at other individuals source code and comparing it to my own, but I still can't get it to work.

Here is the whittled down source code (sorry it's still a bit long, it takes a bit of code to record to a .wav on my own):

// Compile with "g++ test.ccp -o test -lasound"

// Use the newer ALSA API
#define ALSA_PCM_NEW_HW_PARAMS_API

#include <alsa/asoundlib.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdint.h>

struct WaveHeader
{
        char RIFF_marker[4];
        uint32_t file_size;
        char filetype_header[4];
        char format_marker[4];
        uint32_t data_header_length;
        uint16_t format_type;
        uint16_t number_of_channels;
        uint32_t sample_rate;
        uint32_t bytes_per_second;
        uint16_t bytes_per_frame;
        uint16_t bits_per_sample;
};

struct WaveHeader *genericWAVHeader(uint32_t sample_rate, uint16_t bit_depth, uint16_t channels)
{
    struct WaveHeader *hdr;
    hdr = (WaveHeader*) malloc(sizeof(*hdr));
    if (!hdr)
        return NULL;

    memcpy(&hdr->RIFF_marker, "RIFF", 4);
    memcpy(&hdr->filetype_header, "WAVE", 4);
    memcpy(&hdr->format_marker, "fmt ", 4);
    hdr->data_header_length = 16;
    hdr->format_type = 1;
    hdr->number_of_channels = channels;
    hdr->sample_rate = sample_rate;
    hdr->bytes_per_second = sample_rate * channels * bit_depth / 8;
    hdr->bytes_per_frame = channels * bit_depth / 8;
    hdr->bits_per_sample = bit_depth;

    return hdr;
}

int writeWAVHeader(int fd, struct WaveHeader *hdr)
{
    if (!hdr)
        return -1;

    write(fd, &hdr->RIFF_marker, 4);
    write(fd, &hdr->file_size, 4);
    write(fd, &hdr->filetype_header, 4);
    write(fd, &hdr->format_marker, 4);
    write(fd, &hdr->data_header_length, 4);
    write(fd, &hdr->format_type, 2);
    write(fd, &hdr->number_of_channels, 2);
    write(fd, &hdr->sample_rate, 4);
    write(fd, &hdr->bytes_per_second, 4);
    write(fd, &hdr->bytes_per_frame, 2);
    write(fd, &hdr->bits_per_sample, 2);
    write(fd, "data", 4);

    uint32_t data_size = hdr->file_size + 8 - 44;
    write(fd, &data_size, 4);

    return 0;
}

int recordWAV(const char *fileName, struct WaveHeader *hdr, uint32_t duration)
{
    int err;
    int size;
    snd_pcm_t *handle;
    snd_pcm_hw_params_t *params;
    unsigned int sampleRate = hdr->sample_rate;
    int dir;
    snd_pcm_uframes_t frames = 32;
    char *device = (char*) "plughw:1,0";
    char *buffer;
    int filedesc;

    printf("Capture device is %s\n", device);

    /* Open PCM device for recording (capture). */
    err = snd_pcm_open(&handle, device, SND_PCM_STREAM_CAPTURE, 0);
    if (err)
    {
        fprintf(stderr, "Unable to open PCM device: %s\n", snd_strerror(err));
        return err;
    }

    /* Allocate a hardware parameters object. */
    snd_pcm_hw_params_alloca(&params);

    /* Fill it in with default values. */
    snd_pcm_hw_params_any(handle, params);

    /* ### Set the desired hardware parameters. ### */

    /* Interleaved mode */
    err = snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);
    if (err)
    {
        fprintf(stderr, "Error setting interleaved mode: %s\n", snd_strerror(err));
        snd_pcm_close(handle);
        return err;
    }
    /* Signed 16-bit little-endian format */
    if (hdr->bits_per_sample == 16) err = snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE);
    else err = snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_U8);
    if (err)
    {
        fprintf(stderr, "Error setting format: %s\n", snd_strerror(err));
        snd_pcm_close(handle);
        return err;
    }
    /* Two channels (stereo) */
    err = snd_pcm_hw_params_set_channels(handle, params, hdr->number_of_channels);
    if (err)
    {
        fprintf(stderr, "Error setting channels: %s\n", snd_strerror(err));
        snd_pcm_close(handle);
        return err;
    }
    /* 44100 bits/second sampling rate (CD quality) */
    sampleRate = hdr->sample_rate;
    err = snd_pcm_hw_params_set_rate_near(handle, params, &sampleRate, &dir);
    if (err)
    {
        fprintf(stderr, "Error setting sampling rate (%d): %s\n", sampleRate, snd_strerror(err));
        snd_pcm_close(handle);
        return err;
    }
    hdr->sample_rate = sampleRate;
    /* Set period size*/
    err = snd_pcm_hw_params_set_period_size_near(handle, params, &frames, &dir);
    if (err)
    {
        fprintf(stderr, "Error setting period size: %s\n", snd_strerror(err));
        snd_pcm_close(handle);
        return err;
    }
    /* Write the parameters to the driver */
    err = snd_pcm_hw_params(handle, params);
    if (err < 0)
    {
        fprintf(stderr, "Unable to set HW parameters: %s\n", snd_strerror(err));
        snd_pcm_close(handle);
        return err;
    }

    /* Use a buffer large enough to hold one period */
    err = snd_pcm_hw_params_get_period_size(params, &frames, &dir);
    if (err)
    {
        fprintf(stderr, "Error retrieving period size: %s\n", snd_strerror(err));
        snd_pcm_close(handle);
        return err;
    }

    size = frames * hdr->bits_per_sample / 8 * hdr->number_of_channels; /* 2 bytes/sample, 2 channels */
    buffer = (char *) malloc(size);
    if (!buffer)
    {
        fprintf(stdout, "Buffer error.\n");
        snd_pcm_close(handle);
        return -1;
    }

    err = snd_pcm_hw_params_get_period_time(params, &sampleRate, &dir);
    if (err)
    {
        fprintf(stderr, "Error retrieving period time: %s\n", snd_strerror(err));
        snd_pcm_close(handle);
        free(buffer);
        return err;
    }

    uint32_t pcm_data_size = hdr->sample_rate * hdr->bytes_per_frame * duration / 1000;
    hdr->file_size = pcm_data_size + 44 - 8;

    filedesc = open(fileName, O_WRONLY | O_CREAT, 0644);
    err = writeWAVHeader(filedesc, hdr);
    if (err)
    {
        fprintf(stderr, "Error writing .wav header.");
        snd_pcm_close(handle);
        free(buffer);
        close(filedesc);
        return err;
    }
    fprintf(stdout, "Channels: %d\n", hdr->number_of_channels);
    for(int i = duration * 1000 / sampleRate; i > 0; i--)
    {
        err = snd_pcm_readi(handle, buffer, frames);
        if (err == -EPIPE) fprintf(stderr, "Overrun occurred: %d\n", err);
        if (err) err = snd_pcm_recover(handle, err, 0);
        // Still an error, need to exit.
        if (err)
        {
            fprintf(stderr, "Error occured while recording: %s\n", snd_strerror(err));
            snd_pcm_close(handle);
            free(buffer);
            close(filedesc);
            return err;
        }
        write(filedesc, buffer, size);
    }

    close(filedesc);
    snd_pcm_drain(handle);
    snd_pcm_close(handle);
    free(buffer);

    printf("Finished writing to %s\n", fileName);
    return 0;
}

int main(int argc, char *argv[]) {

    if(argc != 2)
    {
        fprintf(stderr, "Usage: %s (record duration)\n", argv[0]);
        return -1;
    }

    int err;
    struct WaveHeader *hdr;

    // Creates a temporary file in /tmp

    char wavFile[L_tmpnam + 5];
    char *tempFilenameStub = tmpnam(NULL);
    sprintf(wavFile, "%s.wav", tempFilenameStub);
    hdr = genericWAVHeader(44000, 16, 2);
    if (!hdr)
    {
        fprintf(stderr, "Error allocating WAV header.\n");
        return -1;
    }

    err = recordWAV(wavFile, hdr, 1000 * strtod(argv[1], NULL));
    if (err)
    {
            fprintf(stderr, "Error recording WAV file: %d\n", err);
            return err;
    }

    free(hdr);
    return 0;
}

Output I get when the program is run:

$ ./capture 5
Capture device is plughw:1,0
Channels: 2
Error occured while recording: Channel number out of range
Error recording WAV file: -44

Any suggestions? I've been banging my head on this for a while.

Answer 1

Error codes returned by snd_* functions are negative. There are functions that can return a positive value to indicate success (e.g., snd_pcm_readi returns the number of frames).

Answer 2

TRY THIS:

printf("Channels: %d\n", hdr->number_of_channels);
for (i = 0; i < 2*16000/128; i++)
{
    printf("\n Recording %d",i);
    err = snd_pcm_readi(handle, buffer, frames);
    write(filedesc, buffer, size);
 }