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我正在构建一个应用程序,部分需要将任何不是 44100Hz 的输入 PCM 音频文件重新采样为 44.1(或者至少尽最大努力做到这一点)。
为了处理我正在使用的重采样 soxr 。 soxr 没有依赖项并且是轻量级的,这在这种情况下是理想的,但它不提供 native 文件 I/O。我对 C 语言 IO 流的经验非常有限,所以我遇到了困难。该应用程序是模块化设计的,因此我需要重新采样过程来创建一个输出文件,然后将其传递给其他处理器,而不是简单地直接处理输出流。
为了创建该输出文件,我尝试获取 soxr
重采样过程生成的数据,并将其传递给 libsndfile ,它应该能够将音频写入文件。
下面是对我所处位置的极其详细的解释,尽管我不知道它为什么会崩溃。我怀疑这与缓冲区的分配和使用方式有关。 (注意:在此代码之前正在使用 sndfile 读取输入文件)
(这是整个事情的single gist)
// Use "high quality" resampling
unsigned int q_recipe = SOXR_HQ;
// No
unsigned long q_flags = 0;
// Create the q_spec
soxr_quality_spec_t q_spec = soxr_quality_spec(q_recipe, q_flags);
soxr_datatype_t itype;
// Get the SFINFO format
int iformat = self.inputFileInfo.format;
// Set the soxr itype to the corresponding format
if ((iformat & SF_FORMAT_FLOAT) == SF_FORMAT_FLOAT) {
itype = SOXR_FLOAT32_S;
} else if ((iformat & SF_FORMAT_DOUBLE) == SF_FORMAT_DOUBLE) {
itype = SOXR_FLOAT64_S;
} else if ((iformat & SF_FORMAT_PCM_32) == SF_FORMAT_PCM_32) {
itype = SOXR_INT32_S;
} else {
itype = SOXR_INT16_S;
}
// Always want the output to match the input
soxr_datatype_t otype = itype;
soxr_io_spec_t io_spec = soxr_io_spec(itype, otype);
// A single thread is fine
soxr_runtime_spec_t runtime_spec = soxr_runtime_spec(1);
soxr_error_t error;
// Input rate can be read from the SFINFO
double const irate = self.inputFileInfo.samplerate;
// Output rate is defined elsewhere, but this generally = 44100
double const orate = self.task.resampler.immutableConfiguration.targetSampleRate;
// Channel count also comes from SFINFO
unsigned chans = self.inputFileInfo.channels;
// Put it all together
soxr_t soxr = soxr_create(irate, orate, chans, &error, &io_spec, &q_spec, &runtime_spec);
我对以下任何代码都不太有信心,但我已经三次检查了数学,一切似乎都满足库 API 的期望。
// Frames in sndfile are called Samples in soxr
// One frame is 1 item per channel
// ie frame_items = 1 item * channels
size_t const iframeitems = (1 * chans);
// item size is the data type size of the input type
//
size_t iitemsize;
if ((iformat & SF_FORMAT_FLOAT) == SF_FORMAT_FLOAT) {
iitemsize = sizeof(Float32);
} else if ((iformat & SF_FORMAT_DOUBLE) == SF_FORMAT_DOUBLE) {
iitemsize = sizeof(Float64);
} else if ((iformat & SF_FORMAT_PCM_32) == SF_FORMAT_PCM_32) {
iitemsize = sizeof(int32_t);
} else {
iitemsize = sizeof(int16_t);
}
// frame size is item size * items per frame (channels)
// eg for 2 channel 16 bit, frame size = 2 * 2
size_t const iframesize = (iframeitems * iitemsize);
// Number of frames to read (arbitrary)
sf_count_t const ireqframes = 1024;
// Size of the buffer is number of frames * size per frame
size_t const ibufsize = iframesize * ireqframes;
void *ibuf = malloc(ibufsize);
// Output
//////////////////////////////
// These match the input
size_t const oframeitems = iframeitems;
size_t const oitemsize = iitemsize;
// frame size is item size * items per frame (channels)
size_t const oframesize = (oframeitems * oitemsize);
// Number of frames expected after resampling
// eg
// orate = 44100
// irate = 48000
// ireqframe = 1024
// expect fewer frames (downsample)
// (44100 / 4800) * 1024 = 940.8
// Add 0.5 to deal with rounding?
sf_count_t const oexpframes = (ireqframes * (orate / irate)) + 0.5;
// Size of the buffer is number of frames * size per frame
size_t const obufsize = oframesize * oexpframes;
void *obuf = malloc(obufsize);
// Go
//////////////////////////////
size_t total_resample_output_frame_count = 0;
size_t need_input = 1;
sf_count_t num_frames_written = 0;
do {
sf_count_t num_frames_read = 0;
size_t actual_resample_output_samples = 0;
// Read the input file based on its type
// num_frames_read should be 1024
if (otype == SOXR_INT16_S || otype == SOXR_INT32_S) {
num_frames_read = sf_readf_int(self.inputFile, ibuf, ireqframes);
} else if (otype == SOXR_FLOAT32_S) {
num_frames_read = sf_readf_float(self.inputFile, ibuf, ireqframes);
} else {
num_frames_read = sf_readf_double(self.inputFile, ibuf, ireqframes);
}
// If there were no frames left to read we're done
if (num_frames_read == 0) {
// passing NULL input buffer to soxr_process indicates End-of-input
ibuf = NULL;
need_input = 0;
}
// Run the resampling on frames read from the input file
error = soxr_process(soxr, ibuf, num_frames_read, NULL, obuf, oexpframes, &actual_resample_output_samples);
total_resample_output_frame_count += actual_resample_output_samples;
// Write the resulting data to output file
// num_frames_written should = actual_resample_output_samples
if (otype == SOXR_INT16_S || otype == SOXR_INT32_S) {
num_frames_written = sf_writef_int(self.outputFile, obuf, actual_resample_output_samples);
} else if (otype == SOXR_FLOAT32_S) {
num_frames_written = sf_writef_float(self.outputFile, obuf, actual_resample_output_samples);
} else {
num_frames_written = sf_writef_double(self.outputFile, obuf, actual_resample_output_samples);
}
} while (!error && need_input);
soxr_delete(soxr);
free(obuf), free(ibuf);
这为 soxr_process
提供了 EXC_BAD_ACCESS。我现在不知道还能尝试什么。
最佳答案
SOXR_INT32_S
等数据类型中的 _S
表示您正在使用分割 channel ,示例 4-split-channels.c
看来在这种情况下您需要传递一个指针数组,每个 channel 一个。
但是,在上面的代码中,您只传递了单个分配的内存块,因此我猜测您正在期待交错的 channel 数据。也许您可以尝试将 _S
更改为 _I
。
关于c - 使用 soxr 和 libsndfile 重新采样 PCM 文件数据会崩溃,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/26771290/
我正在构建一个应用程序,部分需要将任何不是 44100Hz 的输入 PCM 音频文件重新采样为 44.1(或者至少尽最大努力做到这一点)。 为了处理我正在使用的重采样 soxr 。 soxr 没有依赖
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