wav파일 속도2배속하는 코드 질문합니다!

#include <stdlib.h> 
#include <string.h> 
#include <stdio.h> 
 
typedef unsigned short    uint16_t; 
typedef unsigned int    uint32_t; 
typedef int                int16_t; 
typedef unsigned char    byte; 
 
typedef struct { 
    char     chunk_id[4]; 
    uint32_t chunk_size;  
    char     format[4]; 
    char     fmtchunk_id[4]; 
    uint32_t fmtchunk_size; 
    uint16_t audio_format; 
    uint16_t num_channels; 
    uint32_t sample_rate;  
    uint32_t byte_rate;  
    uint16_t block_align; 
    uint16_t bps; 
    char     datachunk_id[4];  
 
    uint32_t datachunk_size; 
 }WavHeader;  
 
 int total_file_len = 0;
 
 void wav_read(char * file_name, WavHeader * header, byte ** real_data) 
 { 
    FILE * fp; 
    int len; 
    fp = fopen(file_name, "rb"); 
    len = fread(header, 1, sizeof(WavHeader), fp); 
    total_file_len += len; 
 
    (*real_data) = (byte *)malloc(header->datachunk_size); 
    len = fread(*real_data, 1, header->datachunk_size, fp);  
    total_file_len += len; 
    fclose(fp); 
 } 
 
 void wav_write(char * file_name, WavHeader * header, byte * real_data) 
 { 
    FILE * fp; 
    header->datachunk_size /= 2; 
    fp = fopen(file_name, "wb"); 
    fwrite(header, sizeof(WavHeader), 1, fp); 
    byte *r = (byte *)malloc(header->datachunk_size); // 
    for(int i = 0; i< header->datachunk_size; i++) // 
    { 
       *(r+i) = *(real_data + 2*i);  //이부분!! 
    } 
    fwrite(r,header->datachunk_size , 1, fp); 
    free(r); 
    fclose(fp);    
 } 
 
 int main() 
 { 
    WavHeader header; //헤더 
    byte * real_data; //소리데이터 
    wav_read("a.wav", &header, &real_data); 
    wav_write("write.wav", &header, real_data); 
    free(real_data); 
    return 0; 
 
 }