Audio resampling bug - c

Question

I'm trying to construct and use a basic audio resampler, taking WAVE file as input, resampling it to defined fs and returning resampled file. The code runs, but it generates inaudible output file that cannot be opened by Windows Media Player. I honestly don't know what causes this.
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include "wavfile.h"
#define FRAME_SIZE 256
void resample(float *in, float *out, int inputFrameSize, int outputFrameSize, float inputFs, float outputFs, float *index, float firstsampleofthenextframe)
{
float increment = inputFs/outputFs;
int i;
float frac;
int intp;
for (i=0;i<outputFrameSize;i++)
{
if ((*index) < inputFrameSize - 1) {
//linear interpolation
intp = (int)(*index);
frac = (*index) - (float)intp;
out[i] = frac * in[intp+1] + (1.0-frac) * in[intp];
} else { //index between inputFrameSize-2 and inputFrameSize-1
intp = (int)(*index);
frac = (*index) - (float)intp;
out[i] = frac * firstsampleofthenextframe + (1.0-frac) * in[intp];
}
//left_out[i] = 0.2*sin(0.001*3.141592635*(*index));
(*index) += increment;
}
}
int main()
{
struct wavfile_header readh;
struct wavfile_header writeh;
float left_in[FRAME_SIZE];
float right_in[FRAME_SIZE];
float left_out[FRAME_SIZE*2];
float right_out[FRAME_SIZE*2];
//float *left_out;
//float *right_out;
float indexL, indexR; //sample index used for interpolation
FILE * infile;
FILE * outfile;
fpos_t position;
int numBytes, numFrames;
int i;
int outFrameSize;
readh.num_channels = 2;
readh.sample_rate = 44100;
writeh.num_channels = 2;
writeh.sample_rate = 48000;
outFrameSize = (int)((float)FRAME_SIZE * (float)(writeh.sample_rate) / (float)(readh.sample_rate));
//left_out = (float*) malloc(sizeof(float)*outFrameSize);
//right_out = (float*) malloc(sizeof(float)*outFrameSize);
infile = wavfile_open_read("input.wav", &readh);
if(!infile) {
printf("read error");
return 1;
}
outfile = wavfile_open_write("output.wav", &writeh);
if(!outfile) {
printf("write error");
return 1;
}
//main processing loop
numBytes = readh.riff_length;
numFrames = numBytes / (2*FRAME_SIZE);
indexL = indexR = 0.f; //start from the 0th sample of the input signal
while(numFrames > 0)
{
float left_overlap, right_overlap;
short sl, sr;
for(i=0;i<FRAME_SIZE;i++) //read frame
{
short sleft, sright;
fread(&sleft ,sizeof(short),1, infile); //deinterleave samples
fread(&sright ,sizeof(short),1, infile);
fflush(infile);
left_in[i] = sleft * 0.0000305185f; // * (1/32767) - 16-bit input automatically normalized to (-1, 1)
right_in[i] = sright * 0.0000305185f; // * (1/32767) - 16-bit input automatically normalized to (-1, 1)
numBytes -= 4;
}
fgetpos (infile, &position);
//one sample ahead is needed to interpolate
fread(&sl ,sizeof(short),1, infile); //deinterleave samples [warning: bug if the input file length is an exact number of frames]
fread(&sr ,sizeof(short),1, infile);
left_overlap = sl * 0.0000305185f; // * (1/32767) - 16-bit input automatically normalized to (-1, 1)
right_overlap = sr * 0.0000305185f; // * (1/32767) - 16-bit input automatically normalized to (-1, 1)
fsetpos (infile, &position);
resample(left_in, left_out, FRAME_SIZE, outFrameSize, 44100, 48000, &indexL, left_overlap);
resample(right_in, right_out, FRAME_SIZE, outFrameSize, 44100, 48000, &indexR, right_overlap);
indexL -= (int)indexL;
indexR -= (int)indexR;
for(i=0;i<outFrameSize;i++) //read frame
{
short left, right;
//left_out[i] = 0.5;
//right_out[i] = 0.5;
left = (short)(left_out[i] * 32767.f);
right = (short)(right_out[i] * 32767.f);
fwrite(&left ,sizeof(short),1, outfile); //deinterleave samples
fwrite(&right ,sizeof(short),1, outfile);
numBytes -= 4;
}
fflush(outfile);
numFrames--;
}
/*
while(numBytes > 0)
{
//below: temp
short left, right;
//left_out[i] = 0.5;
//right_out[i] = 0.5;
left = left_out[i] * 32767;
right = right_out[i] * 32767;
fwrite(&left ,sizeof(short),1, outfile); //deinterleave samples
fwrite(&right ,sizeof(short),1, outfile);
numBytes--;
}
*/
fflush(outfile);
//free(left_out);
//free(right_out);
fclose(outfile);
fclose(infile);
return 0;
}