我正在尝试正确读取WAVE文件,PCM,单声道,16位(每个样本2字节)。我已经成功读取了标题。问题是阅读(写入)数据部分。
据我所知,数据块中的16位样本是little-endian,并“分裂”为两个8位的块。因此,对我来说,读取正确数据的方法应该是:
1.读取文件并将块放入两个不同的int8_t
变量(或std::vector<int8_t>
..)
1.以某种方式“连接”这两个变量,形成一个int16_t
,并能够处理它。
问题是我不知道如何处理小字节序,而且这些样本不是无符号的,所以我不能使用〈〈操作符。
这是我做过的一个试验,没有成功:
int8_t buffer[], firstbyte,secondbyte;
int16_t result;
std::vector<int16_t> data;
while(Read bytes and put them in buffer){
for (int j=0;j<bytesReadFromTheFile;j+=2){
firstbyte = buffer[j];
secondbyte = buffer[j+1];
result = (firstbyte);
result = (result << 8)+secondbyte; //shift first byte and add second
data.push_back(result);
}
}
- 更详细地说 *,我使用了在线找到的这段代码,并从它开始创建了一个类(过程是相同的,但类配置非常长,并且有许多特性对这个问题没有用处):
#include <iostream>
#include <string>
#include <fstream>
#include <cstdint>
using std::cin;
using std::cout;
using std::endl;
using std::fstream;
using std::string;
typedef struct WAV_HEADER
{
/* RIFF Chunk Descriptor */
uint8_t RIFF[4]; // RIFF Header Magic header
uint32_t ChunkSize; // RIFF Chunk Size
uint8_t WAVE[4]; // WAVE Header
/* "fmt" sub-chunk */
uint8_t fmt[4]; // FMT header
uint32_t Subchunk1Size; // Size of the fmt chunk
uint16_t AudioFormat; // Audio format 1=PCM,6=mulaw,7=alaw, 257=IBM Mu-Law, 258=IBM A-Law, 259=ADPCM
uint16_t NumOfChan; // Number of channels 1=Mono 2=Sterio
uint32_t SamplesPerSec; // Sampling Frequency in Hz
uint32_t bytesPerSec; // bytes per second
uint16_t blockAlign; // 2=16-bit mono, 4=16-bit stereo
uint16_t bitsPerSample; // Number of bits per sample
/* "data" sub-chunk */
uint8_t Subchunk2ID[4]; // "data" string
uint32_t Subchunk2Size; // Sampled data length
} wav_hdr;
// Function prototypes
int getFileSize(FILE* inFile);
int main(int argc, char* argv[])
{
wav_hdr wavHeader;
int headerSize = sizeof(wav_hdr), filelength = 0;
const char* filePath;
string input;
if (argc <= 1)
{
cout << "Input wave file name: ";
cin >> input;
cin.get();
filePath = input.c_str();
}
else
{
filePath = argv[1];
cout << "Input wave file name: " << filePath << endl;
}
FILE* wavFile = fopen(filePath, "r");
if (wavFile == nullptr)
{
fprintf(stderr, "Unable to open wave file: %s\n", filePath);
return 1;
}
//Read the header
size_t bytesRead = fread(&wavHeader, 1, headerSize, wavFile);
cout << "Header Read " << bytesRead << " bytes." << endl;
if (bytesRead > 0)
{
//Read the data
uint16_t bytesPerSample = wavHeader.bitsPerSample / 8; //Number of bytes per sample
uint64_t numSamples = wavHeader.ChunkSize / bytesPerSample; //How many samples are in the wav file?
static const uint16_t BUFFER_SIZE = 4096;
int8_t* buffer = new int8_t[BUFFER_SIZE];
while ((bytesRead = fread(buffer, sizeof buffer[0], BUFFER_SIZE / (sizeof buffer[0]), wavFile)) > 0)
{
* /** DO SOMETHING WITH THE WAVE DATA HERE **/ *
cout << "Read " << bytesRead << " bytes." << endl;
}
delete [] buffer;
buffer = nullptr;
filelength = getFileSize(wavFile);
cout << "File is :" << filelength << " bytes." << endl;
cout << "RIFF header :" << wavHeader.RIFF[0] << wavHeader.RIFF[1] << wavHeader.RIFF[2] << wavHeader.RIFF[3] << endl;
cout << "WAVE header :" << wavHeader.WAVE[0] << wavHeader.WAVE[1] << wavHeader.WAVE[2] << wavHeader.WAVE[3] << endl;
cout << "FMT :" << wavHeader.fmt[0] << wavHeader.fmt[1] << wavHeader.fmt[2] << wavHeader.fmt[3] << endl;
cout << "Data size :" << wavHeader.ChunkSize << endl;
// Display the sampling Rate from the header
cout << "Sampling Rate :" << wavHeader.SamplesPerSec << endl;
cout << "Number of bits used :" << wavHeader.bitsPerSample << endl;
cout << "Number of channels :" << wavHeader.NumOfChan << endl;
cout << "Number of bytes per second :" << wavHeader.bytesPerSec << endl;
cout << "Data length :" << wavHeader.Subchunk2Size << endl;
cout << "Audio Format :" << wavHeader.AudioFormat << endl;
// Audio format 1=PCM,6=mulaw,7=alaw, 257=IBM Mu-Law, 258=IBM A-Law, 259=ADPCM
cout << "Block align :" << wavHeader.blockAlign << endl;
cout << "Data string :" << wavHeader.Subchunk2ID[0] << wavHeader.Subchunk2ID[1] << wavHeader.Subchunk2ID[2] << wavHeader.Subchunk2ID[3] << endl;
}
fclose(wavFile);
return 0;
}
// find the file size
int getFileSize(FILE* inFile)
{
int fileSize = 0;
fseek(inFile, 0, SEEK_END);
fileSize = ftell(inFile);
fseek(inFile, 0, SEEK_SET);
return fileSize;
}
问题出在/使用此处的波浪数据执行操作/中。我不知道如何获取样本值。
2条答案
按热度按时间gojuced71#
我是一个Java程序员,不是C++,但我经常处理这个问题。
PCM数据是按帧组织的。如果是单声道、小字节序、16位,第一个字节将是值的下半部分,第二个字节将是值的上半部分,包括符号位。大字节序将反转字节。如果是立体声,完整的帧(我认为是左,然后是右,但我不确定)在移动到下一帧之前完整地呈现。
我对这里显示的所有代码感到有点惊讶。在Java中,下面的代码足以将PCM编码为带符号的值:
IDK如何将其直接翻译成C++,但我们只是简单地将两个字节进行OR运算,第二个字节先向左移8位。纯移位选择符号位。(我不记得为什么包括& 0xff--我很久以前写过这个,它工作正常。)
奇怪为什么这么多的答案都在评论里,而不是作为答案贴出来。我以为评论是为了澄清OP的问题。
n1bvdmb62#
类似这样的方法是可行的:
while循环内部:
然后通过执行以下操作在-1和1之间归一化:
标准化自:sms-tools
注:这适用于采样率为44100,分辨率为16位的单声道文件。