我有一个.wav文件，我想在C ++中读它。 我做的RIFF文件头的一些研究，写了代码加载它。
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
using namespace std;
#define BUFFER_LEN 4096
int main(int argc,char * argv[])
{
// Buffers etc..
char ChunkID[4], Format[4], Subchunk1ID[4],Subchunk2ID[4];
int ChunkSize,Subchunk1Size, SampleRate, ByteRate,Subchunk2Size;
short AudioFormat, NumChannels, BlockAlign, BitsPerSample;
// Read the wave file
FILE *fhandle=fopen(argv[1],"rb");
fread(ChunkID,1,4,fhandle);
fread(&ChunkSize,4,1,fhandle);
fread(Format,1,4,fhandle);
fread(Subchunk1ID,1,4,fhandle);
fread(&Subchunk1Size,4,1,fhandle);
fread(&AudioFormat,2,1,fhandle);
fread(&NumChannels,2,1,fhandle);
fread(&SampleRate,4,1,fhandle);
fread(&ByteRate,4,1,fhandle);
fread(&BlockAlign,2,1,fhandle);
fread(&BitsPerSample,2,1,fhandle);
fread(&Subchunk2ID,1,4,fhandle);
fread(&Subchunk2Size,4,1,fhandle);
fclose(fhandle);
// print RIFF info
printf("\%c",ChunkID[0]);
printf("\%c",ChunkID[1]);
printf("\%c",ChunkID[2]);
printf("\%c",ChunkID[3]);
cout << endl;
// print chunk size
printf("%d",ChunkSize);
cout << endl;
// print format
printf("\%c",Format[0]);
printf("\%c",Format[1]);
printf("\%c",Format[2]);
printf("\%c",Format[3]);
cout << endl;
// print sub chunk 1 ID
printf("\%c",Subchunk1ID[0]);
printf("\%c",Subchunk1ID[1]);
printf("\%c",Subchunk1ID[2]);
printf("\%c",Subchunk1ID[3]);
cout << endl;
// print sub chunk 1 size
printf("%d",Subchunk1Size);
cout << endl;
// print audio format
printf("%hd",AudioFormat);
cout << endl;
// print number of channels
printf("%hd",NumChannels);
cout << endl;
return 0;
}
然而，这是非常有线，我对我的输入文件OS.wav运行这段代码。 它输出的信息：
RIFF
307201488
WAVE
Fake
2
0
28006
你可以看到“FMT”是“假货”。
然后我用SOX通过这个WAV文件转换：
sox OS.wav test.wav
并再次运行我的代码。 它具有信息：
RIFF
307200050
WAVE
fmt
18
3
2
我没有改变任何事情。 但是，标头信息是如此的不同。 谁能告诉我，为什么出现这种情况吗？
谢谢。
你是假设fmt块是内第一子块RIFF/WAVE块。 这不是一个要求或保证。 请在RIFF / WAV格式的一些调查研究。 WAVE子块可以以任何顺序出现，是该唯一的规则fmt块必须在之前出现data块，而其他块可以出现之前，之后，和在它们之间。
分析文件正确的方法是通过子块一次一个循环。 读出的块ID和CHUNKSIZE，然后读取的字节指定数量（考虑填充在内），并且根据需要将块ID处理它们，然后重复直至EOF。 这可以让你处理你感兴趣的块并跳过你不关心的人。 不要做任何假设他们的顺序（但确实验证了一个特殊的情况下），绝对不要假设fmt块是第一块，因为它可能不是。
尝试更多的东西是这样的：
#include <iostream>
#include <istream>
#include <stdexcept>
#include <string>
using namespace std;
struct chunkHdr
{
char id[4];
unsigned int size;
unsigned int pos;
};
bool isChunkID(const chunkHdr &c, char id1, char id2, char id3, char id4)
{
return ((c.id[0] == id1) &&
(c.id[1] == id2) &&
(c.id[2] == id3) &&
(c.id[3] == id4));
}
void read(ifstream &f, void *buffer, streamsize size, chunkHdr *parent)
{
if (!f.read(static_cast<char*>(buffer), size))
{
if (f.eof())
throw runtime_error("Unexpected EOF while reading from file");
throw runtime_error("Unable to read from file");
}
if (parent) parent->pos += size;
}
void skip(ifstream &f, streamsize size, chunkHdr *parent)
{
if (!f.seekg(size, ios_base::cur))
throw runtime_error("Unable to read from file");
if (parent) parent->pos += size;
}
void read(ifstream &f, chunkHdr &c, chunkHdr *parent)
{
read(f, c.id, 4, parent);
read(f, &(c.size), 4, parent);
c.pos = 0;
}
int main(int argc, char * argv[])
{
// Buffers etc..
chunk riff, wave, chk;
bool fmtFound = false;
try
{
// Open the wave file
ifstream wavFile(argv[1], ios_base::binary);
if (!wavFile)
throw runtime_error("Unable to open file");
// check the RIFF header
read(wavFile, riff, NULL);
if (!isChunkID(riff, 'R', 'I', 'F', 'F'))
throw runtime_error("File is not a RIFF file");
cout << "RIFF Size: " << riff.size << endl;
// check the WAVE header
read(wavFile, wave.id, 4, &riff);
wave.size = riff.size - 4;
wave.pos = 0;
cout << "RIFF Type: '" << string(wave.id, 4) << "'" << endl;
if (!isChunkID(wave, 'W', 'A', 'V', 'E'))
throw runtime_error("File is not a WAV file");
// read WAVE chunks
while (wave.pos < wave.size)
{
read(wavFile, chk, &wave);
cout << "Chunk: '" << string(chk.id, 4) << "', Size: " << chk.size << endl;
if (isChunkID(chk, 'f', 'm', 't', ' '))
{
if (fmtFound)
throw runtime_error("More than one FMT chunk encountered");
fmtFound = true;
unsigned int SampleRate, ByteRate;
unsigned short AudioFormat, NumChannels, BlockAlign, BitsPerSample, ExtraSize;
read(wavFile, &AudioFormat, 2, &chk);
read(wavFile, &NumChannels, 2, &chk);
read(wavFile, &SampleRate, 4, &chk);
read(wavFile, &ByteRate, 4, &chk);
read(wavFile, &BlockAlign, 2, &chk);
cout << " Audio Format: " << AudioFormat << endl;
cout << " Channels: " << NumChannels << endl;
cout << " Sample Rate: " << SampleRate << endl;
cout << " Byte Rate: " << ByteRate << endl;
cout << " BlockAlign: " << BlockAlign << endl;
if (chk.size >= 16)
{
read(wavFile, &BitsPerSample, 2, &chk);
cout << " Bits per Sample: " << BitsPerSample << endl;
}
if (chk.size >= 18)
{
read(wavFile, &ExtraSize, 2, &chk);
cout << " Extra Size: " << ExtraSize << endl;
if (ExtraSize > 0)
{
// read and process ExtraSize number of bytes as needed...
skip(wavFile, ExtraSize, &chk);
}
}
if (chk.pos < chk.size)
skip(wavFile, chk.size - chk.pos, &chk);
}
else if (isChunkID(chk, 'd', 'a', 't', 'a'))
{
if (!fmtFound)
throw runtime_error("No FMT chunk encountered before DATA chunk");
// read and process chk.size number of bytes as needed...
skip(wavFile, chk.size, &chk);
}
// read other chunks as needed...
else
{
// skip an unwanted chunk
skip(wavFile, chk.size, &chk);
}
// all done with this chunk
wave.pos += chk.pos;
// check for chunk padding
if (chk.size % 2)
skip(wavFile, 1, &wave);
}
}
catch (const exception &e)
{
cout << "Error! " << e.what() << endl;
}
return 0;
}
