Wave Format - negative data size - format

Question

I'm working with Wave files. I'm reading all the data but in some files data size (specified amount of bytes to be read) is negative, which breaks the reading mechanism. Are wave files constant in terms of byte offsets? Is x offset always the same value?

Answer 1

Since the unit of datasize in the .wav header is unsigned, and since you're getting a signed value, it suggests you're not reading the value from the wave header correctly...

Answer 2

Are wave files constant in terms of byte offsets? Is x offset always
the same value?
No, at least the data section is not always found at the same offset. Some simple programs assume that the sound samples start at a fixed offset (44) but this is not always the case.
The only way to reliably read a wave file is to look for the data section and once you find it, the data size field will be at offset +4 relative to the data section.

Answer 3

If it helps this is what I use for wav decoding/encoding (I coded some years ago):
//---------------------------------------------------------------------------
//--- RIFF WAVE format: 1.01 ------------------------------------------------
//---------------------------------------------------------------------------
#ifndef _RIFF_h
#define _RIFF_h
//---------------------------------------------------------------------------
// 8bit PCM is unsigned
// 16bit PCM is signed 2'os complement little endian (big endian is RIFX)
//---------------------------------------------------------------------------
struct _wave_chunk
{
DWORD ids;
DWORD len;
_wave_chunk(){ ids=' '; len=0; }
_wave_chunk(_wave_chunk& a){ *this=a; }; ~_wave_chunk(){}; _wave_chunk* operator = (const _wave_chunk *a) { *this=*a; return this; }; /*_wave_chunk* operator = (const _wave_chunk &a) { ...copy... return this; };*/
};
struct _wave_hdr
{
DWORD ids; // "RIFF"
DWORD len;
DWORD tps; // "WAVE"
_wave_hdr(){ ids='FFIR'; len=0; tps='EVAW'; }
_wave_hdr(_wave_hdr& a){ *this=a; }; ~_wave_hdr(){}; _wave_hdr* operator = (const _wave_hdr *a) { *this=*a; return this; }; /*_wave_hdr* operator = (const _wave_hdr &a) { ...copy... return this; };*/
};
struct _wave_fmt
{
DWORD ids; // "fmt "
DWORD len; // 16,18,40
WORD format; // 1 = PCM linear quantization
/* 0x0001 WAVE_FORMAT_PCM PCM
0x0003 WAVE_FORMAT_IEEE_FLOAT IEEE float
0x0006 WAVE_FORMAT_ALAW 8-bit ITU-T G.711 A-law
0x0007 WAVE_FORMAT_MULAW 8-bit ITU-T G.711 µ-law
0xFFFE WAVE_FORMAT_EXTENSIBLE Determined by SubFormat */
WORD chanels;
DWORD samplerate;
DWORD byterate;
WORD blockalign;
WORD bits;
WORD ext_len; // extension length 0,22
WORD ext_validbits;
DWORD ext_channelmask;
BYTE ext_subformat[16];
_wave_fmt(){ ids=' tmf'; len=16; format=1; chanels=1; samplerate=44100; bits=8; ext_len=0; ext_validbits=0; ext_channelmask=0; for (int i=0;i<16;i++) ext_subformat[i]=0; compute(); }
_wave_fmt(_wave_fmt& a){ *this=a; }; ~_wave_fmt(){}; _wave_fmt* operator = (const _wave_fmt *a) { *this=*a; return this; }; /*_wave_fmt* operator = (const _wave_fmt &a) { ...copy... return this; };*/
void compute()
{
byterate=(chanels*samplerate*bits)/8;
blockalign=(chanels*bits)/8;
}
};
struct _wave_dat
{
DWORD ids; // "data"
DWORD len;
_wave_dat(){ ids='atad'; len=0; }
_wave_dat(_wave_dat& a){ *this=a; }; ~_wave_dat(){}; _wave_dat* operator = (const _wave_dat *a) { *this=*a; return this; }; /*_wave_dat* operator = (const _wave_dat &a) { ...copy... return this; };*/
};
//---------------------------------------------------------------------------
class wave
{
public:
AnsiString name;
int hnd;
bool readonly;
_wave_hdr hdr;
_wave_fmt fmt;
_wave_dat dat;
wave();
~wave();
void create(AnsiString _name);
void write(BYTE *data,DWORD size);
bool open(AnsiString _name);
DWORD read(BYTE *data,DWORD size);
void close();
};
//---------------------------------------------------------------------------
wave::wave()
{
name=0;
hnd=-1;
readonly=true;
}
//---------------------------------------------------------------------------
wave::~wave()
{
close();
}
//---------------------------------------------------------------------------
void wave::create(AnsiString _name)
{
close();
readonly=true;
// hdr=_wave_hdr();
// fmt=_wave_fmt();
// dat=_wave_dat();
hdr.len=sizeof(hdr)-8;
dat.len=0;
fmt.compute();
name=_name;
hnd=FileCreate(name);
if (hnd<0) return;
FileWrite(hnd,&hdr,sizeof(hdr));
FileWrite(hnd,&fmt,fmt.len+8);
FileWrite(hnd,&dat,sizeof(dat));
readonly=false;
}
//---------------------------------------------------------------------------
bool wave::open(AnsiString _name)
{
close();
readonly=true;
name=_name;
hnd=FileOpen(name,fmOpenRead);
if (hnd<0) return false;
if (FileRead(hnd,&hdr,sizeof(hdr))<sizeof(hdr)){ close(); return false; }
if (hdr.ids!='FFIR') return false;
if (hdr.tps!='EVAW') return false;
_wave_chunk chk;
DWORD sz=sizeof(chk),l;
for(;;)
{
if (FileRead(hnd,&chk,sz)<sz){ close(); return false; }
if (chk.ids==' tmf')
{
fmt.ids=chk.ids;
fmt.len=chk.len;
if (FileRead(hnd,((BYTE*)&fmt)+sz,chk.len)<chk.len){ close(); return false; }
}
else if (chk.ids=='atad')
{
dat.ids=chk.ids;
dat.len=chk.len;
return true;
}
else FileSeek(hnd,int(chk.len),1);
}
}
//---------------------------------------------------------------------------
void wave::write(BYTE *data,DWORD size)
{
if (hnd<0) return;
hdr.len+=size;
dat.len+=size;
if (!readonly) FileWrite(hnd,data,size);
}
//---------------------------------------------------------------------------
DWORD wave::read(BYTE *data,DWORD size)
{
if (hnd<0) return 0;
return FileRead(hnd,data,size);
}
//---------------------------------------------------------------------------
void wave::close()
{
name="";
if (hnd<0) return;
FileSeek(hnd,0,0);
if (!readonly) FileWrite(hnd,&hdr,sizeof(hdr));
FileClose(hnd);
hnd=-1;
}
//---------------------------------------------------------------------------
#endif
//---------------------------------------------------------------------------
it does not support all the formats but should be enough to compare and repair your code resp. extract the addressing ... The code is C++/VCL based so you need to port the binary file access and AnsiString datatype to your environment ...
However negative value suggest you are using signed integers again (just like in your other question) so use unsigned datatype instead ... The offsets in RIFF Wave files are never negative !!!
[Edit1] I updated the code for newer formats.
After adding some extensions (see format info from first xbug's comment under OP) to the Wave format the format fmt chunk can have variable size now. Also they added few other chunks (related to compression) so in order to read reliably you need to pass all the RIFF chunks based on their chunk size until you hit the data chunk your data samples should follow...
My original code was for format 1.0 (as mention it was coded years ago) and did not load newer wave files properly (thx to dsp_user for spotting it). I updated it with the new formating so it should be safe to use again.