mixing wavs

//mix 2 wav file
//http://www.youtube.com/user/thecplusplusguy
#include <iostream>
#include <fstream>
#include <string>
#include <cstring>

bool isBigEndian()
{
    int a=1;
    return !((char*)&a)[0];
}

int convertToInt(char* buffer,int len,bool n=false)
{
    int a=0;
    bool neg;   //we have to manually handle the negative sign in this case
    if(!isBigEndian())
    {
        neg=(buffer[len-1] & 128) ? 1 : 0;
        for(int i=0;i<len;i++)
            ((char*)&a)[i]=buffer[i];
    }else{
        neg=(buffer[0] & 128) ? 1 : 0;
        for(int i=0;i<len;i++)
            ((char*)&a)[sizeof(int)-1-i]=buffer[i];
    }
    if(!n)
        return a;
    else
        return a-(neg ? 65536 : 0);
}

//convert an integer to a char array
void convertToChar(char* buffer,int data,int len)
{
    for(int i=0;i<len;i++)
        buffer[i]=0;
    if(isBigEndian())
    {
        for(int i=0;i<len;i++)
            buffer[sizeof(int)-1-i]=((char*)&data)[i];
    }else{
        for(int i=0;i<len;i++)
            buffer[i]=((char*)&data)[i];
    }
}


//loads the wave file like in the tutorial
char* loadWav(const char* filename,int& ochannels,int& osampleRate,int& osamplesPerSecond,int& osize)
{
    std::ifstream in(filename,std::ios::binary);
    char tmpBuffer[4];
    in.read(tmpBuffer,4);
    if(strncmp(tmpBuffer,"RIFF",4)!=0)
    {
        std::cout << "This is not a valid WAV file (1) " << tmpBuffer[0] << tmpBuffer[1] << tmpBuffer[2] << tmpBuffer[3] << tmpBuffer[4] << '\n';
        return 0;
    }
    in.read(tmpBuffer,4);
    int sizeInBytes=convertToInt(tmpBuffer,4);
    in.read(tmpBuffer,4);
    if(strncmp(tmpBuffer,"WAVE",4)!=0)
    {
        std::cout << "This is not a valid WAV file (2) " << tmpBuffer[0] << tmpBuffer[1] << tmpBuffer[2] << tmpBuffer[3] << tmpBuffer[4] << '\n';
        return 0;
    }
    in.read(tmpBuffer,4);
    if(strncmp(tmpBuffer,"fmt ",4)!=0)
    {
        std::cout << "This is not a valid WAV file (3) " << tmpBuffer[0] << tmpBuffer[1] << tmpBuffer[2] << tmpBuffer[3] << tmpBuffer[4] << '\n';
        return 0;
    }
    in.read(tmpBuffer,4);
    int fmtSize=convertToInt(tmpBuffer,4);
    if(fmtSize!=16)
    {
        std::cout << "Sorry only PCM (not compressed WAV)" << fmtSize << '\n';
        return 0;
    }
    in.read(tmpBuffer,2);
    int PCM=convertToInt(tmpBuffer,2);
    if(PCM!=1)
    {
        std::cout << "Sorry only PCM (not compressed WAV)\n";
        return 0;
    }
    in.read(tmpBuffer,2);
    int channels=convertToInt(tmpBuffer,2);
    in.read(tmpBuffer,4);
    int samples=convertToInt(tmpBuffer,4);
    in.read(tmpBuffer,4);
    int byteRate=convertToInt(tmpBuffer,4);
    in.read(tmpBuffer,2);
    int blockAlign=convertToInt(tmpBuffer,2);
    in.read(tmpBuffer,2);
    int bitsPerSample=convertToInt(tmpBuffer,2);
    in.read(tmpBuffer,4);
    if(strncmp(tmpBuffer,"data",4)!=0)
    {
        std::cout << "This is not a valid WAV file (4) " << tmpBuffer[0] << tmpBuffer[1] << tmpBuffer[2] << tmpBuffer[3] << tmpBuffer[4] << '\n';
        return 0;
    }
    in.read(tmpBuffer,4);
    int dataSize=convertToInt(tmpBuffer,4);
    if(dataSize<=0)
    {
        std::cout << "This is not a valid WAV file (4) " << dataSize << '\n';
        return 0;
    }
    char* data=new char[dataSize];
    in.read(data,dataSize);
    ochannels=channels;
    osampleRate=bitsPerSample;
    osamplesPerSecond=samples;
    osize=dataSize;
    return data;
}

//writes out the file
void writeWAV(const char* filename,char* data,int datasize,const char* original)
{
    std::ifstream in(original,std::ios::binary);
    std::ofstream out(filename,std::ios::binary);
    char header[44];    //no conversation, use the same header as the original file (of course, you might want to change that)
    in.read(header,44);
    out.write(header,44);
    out.write(data,datasize);
    out.close();
    in.close();
}

int main()
{
    int ch1,bps1,sps1,size1;
    int ch2,bps2,sps2,size2;
    char* buf1=loadWav("first.wav",ch1,bps1,sps1,size1);
    char* buf2=loadWav("second.wav",ch2,bps2,sps2,size2);
    char* mixed=NULL;   //mixed, final result
    if(ch1!=ch2 || ch1>=2 || bps1!=bps2 || sps1!=sps2)
    {
        std::cout << "Sorry, in this demonstration the channels, bitpersample samplespersecond have to be equal, and no stereo" << std::endl;
    }else{
        int bytePerSample=bps1/8;
        char buf[2];
        if(size2>size1)
        {
            //swap buffers
            char* tmp=buf1;
            buf1=buf2;
            buf2=tmp;
            //swap size
            int itmp=size1;
            size1=size2;
            size2=itmp;
        }
        mixed=new char[size1];
        for(int i=0;i<size2;i+=bytePerSample)   //either go byte-by-byte, or 2-byte at a loop (depent, if it's 8 bit or 16 bit per sample)
        {
            int sample1,sample2;
            sample1=convertToInt(buf1+i,bytePerSample,true);
            sample2=convertToInt(buf2+i,bytePerSample,true);
            int result=(sample1+sample2)/2; //get the avarage of two
            if(bytePerSample==1 && result>255)  //2^8 - 1
                result=255;
            if(bytePerSample==2 && result>65536) //2^16 - 1
                result=65536;
            convertToChar(buf,result,bytePerSample);
            for(int j=0;j<bytePerSample;j++)
            {
                mixed[i+j]=buf[j];
            }
        }
        for(int i=size2;i<size1;i++)    //copy the rest of the data (if there is)
            mixed[i]=buf1[i];
        writeWAV("mixed.wav",mixed,size1,"first.wav");
        std::cout << "mixed.wav created" << std::endl;
    }
    delete[] mixed;
    delete[] buf1;
    delete[] buf2;

}