WSS File Format: Difference between revisions
(improved description) |
m (→C++ code) |
||
Line 80: | Line 80: | ||
Function returns a short array, same size as it's compressed byte equivalent | Function returns a short array, same size as it's compressed byte equivalent | ||
< | <code><syntaxhighlight> | ||
#define LOG10 2.3025850929940456840 //ln(10) | #define LOG10 2.3025850929940456840 //ln(10) | ||
#define LOG2 1.4426950408889634070 //log2(e) | #define LOG2 1.4426950408889634070 //log2(e) | ||
Line 87: | Line 87: | ||
short* DeCompress(const char *CompressedData,int len) | short* DeCompress(const char *CompressedData,int len) | ||
{ | { | ||
short *snap,*OutputData; | short *snap,*OutputData; | ||
if (!(snap=OutputData=new short[len])) return 0; | if (!(snap=OutputData=new short[len])) return 0; | ||
Line 108: | Line 108: | ||
return snap; | return snap; | ||
} | } | ||
</ | </syntaxhighlight></code> | ||
===C# code=== | ===C# code=== | ||
If the <soundData> is compressed the following (C#) code can be used for decompression: | If the <soundData> is compressed the following (C#) code can be used for decompression: |
Revision as of 23:20, 20 October 2011
Introduction
WSS files are used since OFP times to store sound data and its file format is pretty much like the RIFF WAVE file format used for .wav files.
For the purposes of description here, 'Sound' in both wav or wss is recorded as PCM data in 16 bit 'samples'. The quality of that sound is determined by the frequency of those 'samples' per second, referred to as the SampleRate.
Given this: a few important paramaters are define here:
- BitsPerSample: 16
- BytesPerSample: 2 (Inferred BitsPerSample/8)
File Format
Offset | Datatype | Content | Description |
---|---|---|---|
0 | char[4] | "WSS0" | file signature |
4 | ulong | CompressionType | 0 == none. 8== compressed PCM data |
8 | ushort | format | Always 1 (WAVE_FORMAT_PCM) |
10 | ushort | nChannels | 1=mono, 2=stereo |
12 | ulong | SampleRate | e.g. 44100Hz |
16 | ulong | BytesPerSecond | SampleRate * BlockAlign |
20 | ushort | BlockAlign | nChannels * BytesPerSample |
22 | ushort | BitsPerSecond | usually 16 |
24 | ushort | <unknown> | unknown value |
26 | byte[fileSize-26] | <soundData> | here the PCM data of the sound is stored |
Decompression
Compression consists of single encoded byte 'samples' versus uncompressed short 'samples'. Each byte is, effectively, extrapolated to a short, thus making the compressed BYTE array, and the resulting decompressed SHORT array the same number of elements(length). The length is the remaining file length (in bytes) after the header.
C++ code
Function returns a short array, same size as it's compressed byte equivalent
#define LOG10 2.3025850929940456840 //ln(10)
#define LOG2 1.4426950408889634070 //log2(e)
#define MAGIC_NUMBER ((LOG10*LOG2)/28.12574042515172)
short* DeCompress(const char *CompressedData,int len)
{
short *snap,*OutputData;
if (!(snap=OutputData=new short[len])) return 0;
short LastVal=0;
for (;len--;CompressedData++)
{
if (*CompressedData)
{
double asFloat = abs(*CompressedData) *MAGIC_NUMBER;
double rnd = Round(asFloat);
asFloat = pow(2.0, asFloat - rnd) * pow(2, rnd);// mantissa -
if (*CompressedData < 0) asFloat *= -1;
int asInt = Round(asFloat)+LastVal;
if (asInt > SHRT_MAX ) asInt = SHRT_MAX ;
if (asInt < SHRT_MIN) asInt = SHRT_MIN;
LastVal=(short)asInt;
}
*OutputData++ = LastVal;
}
return snap;
}
C# code
If the <soundData> is compressed the following (C#) code can be used for decompression:
PCMData = new Int16[soundData.Length]; for (int j = 0; j < PCMData.Length; j++) { SByte srcSample = (SByte)soundData[j]; if (srcSample != 0) { double asFloat = Math.Abs(srcSample) / 28.12574042515172; asFloat *= 2.3025850929940456840; //ln(10) asFloat *= 1.4426950408889634070; //log2(e) double rnd = Math.Round(asFloat); double mantisse = Math.Pow(2.0, asFloat - rnd); asFloat = mantisse * Math.Pow(2, rnd); if (srcSample < 0) asFloat *= -1; Int32 asInt = (int)Math.Round(asFloat); asInt = (j == 0) ? asInt : (asInt + PCMData[j - 1]); if (asInt > short.MaxValue) asInt = short.MaxValue; if (asInt < short.MinValue) asInt = short.MinValue; PCMData[j] = (Int16)asInt; } else PCMData[j] = (j == 0) ? (Int16)0 : PCMData[j - 1]; }