编辑：我已经更新了以下代码，类似于我所取得的进展。我正在尝试自己编写.wav标题。截至目前，代码无法正常工作，音频未正确写入文件。该代码不包含任何将其转换为.flac文件的尝试。
我正在使用Raspberry Pi（Debian Linux）来录制ALSA library的音频。录音工作正常，但我需要将输入音频编码为FLAC编解码器。
这是我迷路的地方。我花了相当多的时间试图弄清楚如何将这些原始数据转换为FLAC，但我不断提出如何将.wav文件转换为.flac文件的示例。
以下是我用ALSA录制音频的当前（更新的）代码（可能有点粗糙，我仍然在使用C ++）：
// Use the newer ALSA API
#define ALSA_PCM_NEW_HW_PARAMS_API
#include <alsa/asoundlib.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct Riff
{
char chunkId[4]; // "RIFF" (assuming char is 8 bits)
int chunkSize; // (assuming int is 32 bits)
char format[4]; // "WAVE"
};
struct Format
{
char chunkId[4]; // "fmt "
int chunkSize;
short format; // assuming short is 16 bits
short numChannels;
int sampleRate;
int byteRate;
short align;
short bitsPerSample;
};
struct Data
{
char chunkId[4]; // "data"
int chunkSize; // length of data
char* data;
};
struct Wave // Actual structure of a PCM WAVE file
{
Riff riffHeader;
Format formatHeader;
Data dataHeader;
};
int main(int argc, char *argv[])
{
void saveWaveFile(struct Wave *waveFile);
long loops;
int rc;
int size;
snd_pcm_t *handle;
snd_pcm_hw_params_t *params;
unsigned int sampleRate = 44100;
int dir;
snd_pcm_uframes_t frames;
char *buffer;
char *device = (char*) "plughw:1,0";
//char *device = (char*) "default";
printf("Capture device is %s\n", device);
/* Open PCM device for recording (capture). */
rc = snd_pcm_open(&handle, device, SND_PCM_STREAM_CAPTURE, 0);
if (rc < 0)
{
fprintf(stderr, "Unable to open PCM device: %s\n", snd_strerror(rc));
exit(1);
}
/* Allocate a hardware parameters object. */
snd_pcm_hw_params_alloca(¶ms);
/* Fill it in with default values. */
snd_pcm_hw_params_any(handle, params);
/* Set the desired hardware parameters. */
/* Interleaved mode */
snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);
/* Signed 16-bit little-endian format */
snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE);
/* Two channels (stereo) */
snd_pcm_hw_params_set_channels(handle, params, 2);
/* 44100 bits/second sampling rate (CD quality) */
snd_pcm_hw_params_set_rate_near(handle, params, &sampleRate, &dir);
/* Set period size to 32 frames. */
frames = 32;
snd_pcm_hw_params_set_period_size_near(handle, params, &frames, &dir);
/* Write the parameters to the driver */
rc = snd_pcm_hw_params(handle, params);
if (rc < 0)
{
fprintf(stderr, "Unable to set HW parameters: %s\n", snd_strerror(rc));
exit(1);
}
/* Use a buffer large enough to hold one period */
snd_pcm_hw_params_get_period_size(params, &frames, &dir);
size = frames * 4; /* 2 bytes/sample, 2 channels */
buffer = (char *) malloc(size);
/* We want to loop for 5 seconds */
snd_pcm_hw_params_get_period_time(params, &sampleRate, &dir);
loops = 5000000 / sampleRate;
while (loops > 0)
{
loops--;
rc = snd_pcm_readi(handle, buffer, frames);
if (rc == -EPIPE)
{
/* EPIPE means overrun */
fprintf(stderr, "Overrun occurred.\n");
snd_pcm_prepare(handle);
} else if (rc < 0)
{
fprintf(stderr, "Error from read: %s\n", snd_strerror(rc));
} else if (rc != (int)frames)
{
fprintf(stderr, "Short read, read %d frames.\n", rc);
}
if (rc != size) fprintf(stderr, "Short write: wrote %d bytes.\n", rc);
}
Wave wave;
strcpy(wave.riffHeader.chunkId, "RIFF");
wave.riffHeader.chunkSize = 36 + size;
strcpy(wave.riffHeader.format, "WAVE");
strcpy(wave.formatHeader.chunkId, "fmt");
wave.formatHeader.chunkSize = 16;
wave.formatHeader.format = 1; // PCM, other value indicates compression
wave.formatHeader.numChannels = 2; // Stereo
wave.formatHeader.sampleRate = sampleRate;
wave.formatHeader.byteRate = sampleRate * 2 * 2;
wave.formatHeader.align = 2 * 2;
wave.formatHeader.bitsPerSample = 16;
strcpy(wave.dataHeader.chunkId, "data");
wave.dataHeader.chunkSize = size;
wave.dataHeader.data = buffer;
saveWaveFile(&wave);
snd_pcm_drain(handle);
snd_pcm_close(handle);
free(buffer);
return 0;
}
void saveWaveFile(struct Wave *waveFile)
{
FILE *file = fopen("test.wav", "wb");
size_t written;
if (file == NULL)
{
fprintf(stderr, "Cannot open file for writing.\n");
exit(1);
}
written = fwrite(waveFile, sizeof waveFile[0], 1, file);
fclose(file);
if (written < 1);
{
fprintf(stderr, "Writing to file failed, error %d.\n", written);
exit(1);
}
}
如何将PCM数据转换为FLAC并将其保存到磁盘供以后使用？我已经下载了libflac-dev，只需要一个例子即可。
我现在这样做的方式：
./capture > test.raw // or ./capture > test.flac
它的方式（程序为我做的一切）：
./capture
答案 0 :(得分：3)
如果我理解FLAC::Encoder::File文档，您可以执行类似
#include <FLAC++/encoder.h>
FLAC::Encoder::File encoder;
encoder.init("outfile.flac");
encoder.process(buffer, samples);
encoder.finish();
其中buffer是32位整数指针的数组（大小为samples）。
不幸的是，我对音频编码几乎一无所知，所以我不能说任何其他选项。祝你好运！
答案 1 :(得分：2)
请参阅以下代码：
此示例使用wav文件作为输入，然后将其编码为FLAC。
据我了解，黑莓WAV文件与您的RAW数据没有重大区别，我认为您可以修改此代码直接读取“缓冲区”并进行转换。您已经拥有所有相关信息（频道/比特率等），因此删除WAV标题阅读代码应该不会有太大问题。
答案 2 :(得分：1)
请注意：这是来自git repo的Flac Encoder样本的修改版本。
它包含一些关于如何将其更改为OP要求的注释和提示，整个来源将有点长。
请注意，这是C API，它往往比C ++复杂一点。但是一旦你明白了，就很容易在两者之间进行转换。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "share/compat.h"
#include "FLAC/metadata.h"
#include "FLAC/stream_encoder.h"
/* this call back is what tells your program the progress that the encoder has made */
static void progress_callback(const FLAC__StreamEncoder *encoder, FLAC__uint64 bytes_written, FLAC__uint64 samples_written, unsigned frames_written, unsigned total_frames_estimate, void *client_data);
#define READSIZE 1024
static unsigned total_samples = 0; /* can use a 32-bit number due to WAVE size limitations */
/* buffer is where we record to, in your case what ALSA writes to */
/* Note the calculation here to take the total bytes that the buffer takes */
static FLAC__byte buffer[READSIZE/*samples*/ * 2/*bytes_per_sample*/ * 2/*channels*/];
/* pcm is input to FLAC encoder */
/* the PCM data should be here, bps is 4 here...but we are allocating ints! */
static FLAC__int32 pcm[READSIZE/*samples*/ * 2/*channels*/];
int main(int argc, char *argv[])
{
FLAC__bool ok = true;
FLAC__StreamEncoder *encoder = 0;
FLAC__StreamEncoderInitStatus init_status;
FLAC__StreamMetadata *metadata[2];
FLAC__StreamMetadata_VorbisComment_Entry entry;
FILE *fin;
unsigned sample_rate = 0;
unsigned channels = 0;
unsigned bps = 0;
if((fin = fopen(argv[1], "rb")) == NULL) {
fprintf(stderr, "ERROR: opening %s for output\n", argv[1]);
return 1;
}
/* set sample rate, bps, total samples to encode here, these are dummy values */
sample_rate = 44100;
channels = 2;
bps = 16;
total_samples = 5000;
/* allocate the encoder */
if((encoder = FLAC__stream_encoder_new()) == NULL) {
fprintf(stderr, "ERROR: allocating encoder\n");
fclose(fin);
return 1;
}
ok &= FLAC__stream_encoder_set_verify(encoder, true);
ok &= FLAC__stream_encoder_set_compression_level(encoder, 5);
ok &= FLAC__stream_encoder_set_channels(encoder, channels);
ok &= FLAC__stream_encoder_set_bits_per_sample(encoder, bps);
ok &= FLAC__stream_encoder_set_sample_rate(encoder, sample_rate);
ok &= FLAC__stream_encoder_set_total_samples_estimate(encoder, total_samples);
/* sample adds meta data here I've removed it for clarity */
/* initialize encoder */
if(ok) {
/* client data is whats the progress_callback is called with, any objects you need to update on callback can be passed thru this pointer */
init_status = FLAC__stream_encoder_init_file(encoder, argv[2], progress_callback, /*client_data=*/NULL);
if(init_status != FLAC__STREAM_ENCODER_INIT_STATUS_OK) {
fprintf(stderr, "ERROR: initializing encoder: %s\n", FLAC__StreamEncoderInitStatusString[init_status]);
ok = false;
}
}
/* read blocks of samples from WAVE file and feed to encoder */
if(ok) {
size_t left = (size_t)total_samples;
while(ok && left) {
/* record using ALSA and set SAMPLES_IN_BUFFER */
/* convert the packed little-endian 16-bit PCM samples from WAVE into an interleaved FLAC__int32 buffer for libFLAC */
/* why? because bps=2 means that we are dealing with short int(16 bit) samples these are usually signed if you do not explicitly say that they are unsigned */
size_t i;
for(i = 0; i < SAMPLES_IN_BUFFER*channels; i++) {
/* THIS. this isn't the only way to convert between formats, I do not condone this because at first the glance the code seems like it's processing two channels here, but it's not it's just copying 16bit data to an int array, I prefer to use proper type casting, none the less this works so... */
pcm[i] = (FLAC__int32)(((FLAC__int16)(FLAC__int8)buffer[2*i+1] << 8) | (FLAC__int16)buffer[2*i]);
}
/* feed samples to encoder */
ok = FLAC__stream_encoder_process_interleaved(encoder, pcm, SAMPLES_IN_BUFFER);
left-=SAMPLES_IN_BUFFER;
}
}
ok &= FLAC__stream_encoder_finish(encoder);
fprintf(stderr, "encoding: %s\n", ok? "succeeded" : "FAILED");
fprintf(stderr, " state: %s\n", FLAC__StreamEncoderStateString[FLAC__stream_encoder_get_state(encoder)]);
FLAC__stream_encoder_delete(encoder);
fclose(fin);
return 0;
}
/* the updates from FLAC's encoder system comes here */
void progress_callback(const FLAC__StreamEncoder *encoder, FLAC__uint64 bytes_written, FLAC__uint64 samples_written, unsigned frames_written, unsigned total_frames_estimate, void *client_data)
{
(void)encoder, (void)client_data;
fprintf(stderr, "wrote %" PRIu64 " bytes, %" PRIu64 "/%u samples, %u/%u frames\n", bytes_written, samples_written, total_samples, frames_written, total_frames_estimate);
}