录制成WAV文件 [英] Record into WAV file

问题描述

自从我发布了这个问题以来，我一直在尝试写来自原始 PCM 数据的有效 WAV 文件.我已经设法编写了 FLAC 转换器(经过测试并有效)，但它没有对我一直在编写的 WAV 文件进行编码.

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.

我不确定我做错了什么.我一直在网上搜索 其他人 源代码 并将其与我自己的进行比较，但我仍然可以不让它工作.

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.

这是精简后的源代码(抱歉还是有点长，我自己录制到.wav需要一些代码):

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
", 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
", 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
", 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
", 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
", 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
", 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
", 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
", 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
", 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.
");
        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
", 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
", 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
", 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
", 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
", fileName);
    return 0;
}

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

    if(argc != 2)
    {
        fprintf(stderr, "Usage: %s (record duration)
", 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.
");
        return -1;
    }

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

    free(hdr);
    return 0;
}

程序运行时得到的输出:

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

有什么建议吗?我已经为此纠结了一段时间.

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

推荐答案

snd_* 函数返回的错误代码是否定的.有些函数可以返回一个正值来表示成功(例如，snd_pcm_readi 返回帧数).

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).

这篇关于录制成WAV文件的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！