主要是了解一下一般的录音的用户层是如何操作的；
#include <tinyalsa/asoundlib.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <signal.h>
#include <string.h>
#include <limits.h>
#define ID_RIFF 0x46464952
#define ID_WAVE 0x45564157
#define ID_FMT 0x20746d66
#define ID_DATA 0x61746164
#define FORMAT_PCM 1
struct wav_header {
uint32_t riff_id;
uint32_t riff_sz;
uint32_t riff_fmt;
uint32_t fmt_id;
uint32_t fmt_sz;
uint16_t audio_format;
uint16_t num_channels;
uint32_t sample_rate;
uint32_t byte_rate;
uint16_t block_align;
uint16_t bits_per_sample;
uint32_t data_id;
uint32_t data_sz;
};
int capturing = 1;
int prinfo = 1;
unsigned int capture_sample(FILE *file, unsigned int card, unsigned int device,
unsigned int channels, unsigned int rate,
enum pcm_format format, unsigned int period_size,
unsigned int period_count, unsigned int capture_time);
void sigint_handler(int sig)
{
if (sig == SIGINT){
capturing = 0;
}
}
int main(int argc, char **argv)
{
FILE *file;
struct wav_header header;
unsigned int card = 0;
unsigned int device = 0;
unsigned int channels = 2;
unsigned int rate = 48000;
unsigned int bits = 16;
unsigned int frames;
unsigned int period_size = 1024;
unsigned int period_count = 4;
unsigned int capture_time = UINT_MAX;
enum pcm_format format;
int no_header = 0;
if (argc < 2) {
fprintf(stderr, "Usage: %s {file.wav | --} [-D card] [-d device] [-c channels] "
"[-r rate] [-b bits] [-p period_size] [-n n_periods] [-t time_in_seconds]\n\n"
"Use -- for filename to send raw PCM to stdout\n", argv[0]);
return 1;
}
if (strcmp(argv[1],"--") == 0) { // 输出到标准输出
file = stdout;
prinfo = 0;
no_header = 1;
} else {
file = fopen(argv[1], "wb"); // 打开文件
if (!file) {
fprintf(stderr, "Unable to create file '%s'\n", argv[1]);
return 1;
}
}
/* parse command line arguments */ // 命令行数据解析
argv += 2;
while (*argv) {
if (strcmp(*argv, "-d") == 0) {
argv++;
if (*argv)
device = atoi(*argv);
} else if (strcmp(*argv, "-c") == 0) {
argv++;
if (*argv)
channels = atoi(*argv);
} else if (strcmp(*argv, "-r") == 0) {
argv++;
if (*argv)
rate = atoi(*argv);
} else if (strcmp(*argv, "-b") == 0) {
argv++;
if (*argv)
bits = atoi(*argv);
} else if (strcmp(*argv, "-D") == 0) {
argv++;
if (*argv)
card = atoi(*argv);
} else if (strcmp(*argv, "-p") == 0) {
argv++;
if (*argv)
period_size = atoi(*argv);
} else if (strcmp(*argv, "-n") == 0) {
argv++;
if (*argv)
period_count = atoi(*argv);
} else if (strcmp(*argv, "-t") == 0) {
argv++;
if (*argv)
capture_time = atoi(*argv);
}
if (*argv)
argv++;
}
header.riff_id = ID_RIFF;
header.riff_sz = 0;
header.riff_fmt = ID_WAVE;
header.fmt_id = ID_FMT;
header.fmt_sz = 16;
header.audio_format = FORMAT_PCM;
header.num_channels = channels;
header.sample_rate = rate;
switch (bits) {
case 32:
format = PCM_FORMAT_S32_LE;
break;
case 24:
format = PCM_FORMAT_S24_LE;
break;
case 16:
format = PCM_FORMAT_S16_LE;
break;
default:
fprintf(stderr, "%u bits is not supported.\n", bits);
fclose(file);
return 1;
}
header.bits_per_sample = pcm_format_to_bits(format);
header.byte_rate = (header.bits_per_sample / 8) * channels * rate;
header.block_align = channels * (header.bits_per_sample / 8);
header.data_id = ID_DATA;
/* leave enough room for header */
if (!no_header) { // 跳过文件头
fseek(file, sizeof(struct wav_header), SEEK_SET);
}
/* install signal handler and begin capturing */
signal(SIGINT, sigint_handler); // 允许中断程序
frames = capture_sample(file, card, device, header.num_channels,
header.sample_rate, format,
period_size, period_count, capture_time);
if (prinfo) {
printf("Captured %u frames\n", frames);
}
/* write header now all information is known */
if (!no_header) { // 写入文件头
header.data_sz = frames * header.block_align;
header.riff_sz = header.data_sz + sizeof(header) - 8;
fseek(file, 0, SEEK_SET);
fwrite(&header, sizeof(struct wav_header), 1, file);
}
fclose(file);
return 0;
}
unsigned int capture_sample(FILE *file, unsigned int card, unsigned int device,
unsigned int channels, unsigned int rate,
enum pcm_format format, unsigned int period_size,
unsigned int period_count, unsigned int capture_time)
{
struct pcm_config config;
struct pcm *pcm;
char *buffer;
unsigned int size;
unsigned int frames_read;
unsigned int total_frames_read;
unsigned int bytes_per_frame;
memset(&config, 0, sizeof(config));
config.channels = channels;
config.rate = rate;
config.period_size = period_size;
config.period_count = period_count;
config.format = format;
config.start_threshold = 0;
config.stop_threshold = 0;
config.silence_threshold = 0;
pcm = pcm_open(card, device, PCM_IN, &config); // 打开PCM Capture设备
if (!pcm || !pcm_is_ready(pcm)) {
fprintf(stderr, "Unable to open PCM device (%s)\n",
pcm_get_error(pcm));
return 0;
}
size = pcm_frames_to_bytes(pcm, pcm_get_buffer_size(pcm));
buffer = malloc(size);
if (!buffer) {
fprintf(stderr, "Unable to allocate %u bytes\n", size);
pcm_close(pcm);
return 0;
}
if (prinfo) {
printf("Capturing sample: %u ch, %u hz, %u bit\n", channels, rate,
pcm_format_to_bits(format));
}
bytes_per_frame = pcm_frames_to_bytes(pcm, 1);
total_frames_read = 0;
frames_read = 0;
while (capturing) {
frames_read = pcm_readi(pcm, buffer, pcm_get_buffer_size(pcm)); // 获取一帧数据
total_frames_read += frames_read;
if ((total_frames_read / rate) >= capture_time) {
capturing = 0;
}
if (fwrite(buffer, bytes_per_frame, frames_read, file) != frames_read) { // 写入一帧数据到文件
fprintf(stderr,"Error capturing sample\n");
break;
}
}
free(buffer);
pcm_close(pcm);
return total_frames_read;
}