I have a requirement, where I need to write a wav (with pcma data) file multiple times.
Say I have a file audio-g711a.wav. I want to write it to a new file say audio-g711a-out.wav 2 times. When I play audio-g711a-out.wav , it should play twice the longer duration than that of original file.
I did write using below code. However it plays for exactly same duration as that of original file (I was expecting it to play double the duration).
Code is as below.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <pthread.h>
#include <unistd.h>
#include <sys/uio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
int g_count = 0;
void init_config(int argc,char **argv);
void rewrite_file(int count);
int main(int argc, char **argv)
{
init_config(argc, argv);
printf("Count = %d\n", g_count);
rewrite_file(g_count);
return 0;
}
void rewrite_file(int count)
{
int index;
char arr[101];
FILE *fd_in;
FILE *fd_out;
size_t len;
unsigned long chunk_size;
index = 0;
fd_in = fopen("./audio-g711a.wav", "r");
fd_out = fopen("./audio-g711a-out.wav", "w+");
rw_again:
index++;
len = fread(arr, 1, 100, fd_in);
while(len == 100)
{
fwrite(arr, 1, 100, fd_out);
len = fread(arr, 1, 100, fd_in);
}
fwrite(arr, 1, len, fd_out);
if(count > index)
{
printf("Completed %d round of operation of %d total rounds.\n", index, count);
fclose(fd_in);
fd_in = fopen("./audio-g711a.wav", "r");
goto rw_again;
}
return;
}
void init_config(int argc,char **argv)
{
int ch;
while ((ch = getopt(argc, argv, "v:n:N:X")) != -1)
{
switch (ch)
{
case 'n':
case 'N':
{
g_count = atoi(optarg);
}
break;
default:
break;
}
}
return;
}
To execute this, one can execute like ./a.out -n 2
After some R&D, I realized wav files have some sort of header. When I write second time, I am writing the header again. That may cause the file not to play further. I stopped writing the header part (44 bytes) while writing second time. This did not solve the issue.
Can somebody please guide me how can I achieve writing a wav file for at least 2 times.
Update
The working code is as given below.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <pthread.h>
#include <unistd.h>
#include <sys/uio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
int g_count = 0;
void init_config(int argc,char **argv);
void rewrite_file(int count);
int main(int argc, char **argv)
{
init_config(argc, argv);
printf("Count = %d\n", g_count);
rewrite_file(g_count);
return 0;
}
void rewrite_file(int count)
{
int index;
char arr[101];
FILE *fd_in;
FILE *fd_out;
size_t len;
unsigned short data_index = 0;
index = 0;
fd_in = fopen("./audio-g711a.wav", "r");
fd_out = fopen("./audio-g711a-out.wav", "w+");
// copy header
len = fread(arr, 1, 40, fd_in);
fwrite(arr, 1, len, fd_out);
if( strncmp("data", (arr+36), 4) == 0 )
{
data_index = 40;
}
else
{
len = fread(arr, 1, 14, fd_in);
fwrite(arr, 1, len, fd_out);
if( strncmp("data", (arr+10), 4) == 0 )
{
data_index = 54;
}
}
// update header
uint32_t dl;
fseek(fd_in, data_index, SEEK_SET);
fseek(fd_out, data_index, SEEK_SET);
fread(&dl, sizeof(dl), 1, fd_in);
dl *= count;
fwrite(&dl, sizeof(dl), 1, fd_out);
// copy data
rw_again:
index++;
fseek(fd_in, (4 + data_index), SEEK_SET);
len = fread(arr, 1, 100, fd_in);
while(len > 0)
{
fwrite(arr, 1, len, fd_out);
len = fread(arr, 1, 100, fd_in);
}
fwrite(arr, 1, len, fd_out);
if(count > index)
{
printf("Completed %d round of operation of %d total rounds.\n", index, count);
fclose(fd_in);
fd_in = fopen("./audio-g711a.wav", "r");
goto rw_again;
}
fclose(fd_in);
fclose(fd_out);
return;
}
void init_config(int argc,char **argv)
{
int ch;
while ((ch = getopt(argc, argv, "v:n:N:X")) != -1)
{
switch (ch)
{
case 'n':
case 'N':
{
g_count = atoi(optarg);
}
break;
default:
break;
}
}
return;
}
The wav file has a header and a data section:
[HEADER][DATA]
A simple copy, as you do, produces the following file format:
[HEADER][DATA][HEADER][DATA]
What you need is:
[HEADER][DATADATA]
^
|
+--- chunksize at offset 40 updated
Here is a quick hack:
void rewrite_file(int count)
{
int index;
char arr[101];
FILE *fd_in;
FILE *fd_out;
size_t len;
unsigned long chunk_size;
index = 0;
fd_in = fopen("./audio-g711a.wav", "r");
fd_out = fopen("./audio-g711a-out.wav", "w+");
// copy header
len = fread(arr, 1, 40, fd_in);
fwrite(arr, 1, len, fd_out);
// update header
uint32_t dl;
fseek(fd_in, 40, SEEK_SET);
fseek(fd_out, 40, SEEK_SET);
fread(&dl, sizeof(dl), 1, fd_in);
dl *= count;
fwrite(&dl, sizeof(dl), 1, fd_out);
// copy data
rw_again:
index++;
fseek(fd_in, 44, SEEK_SET);
len = fread(arr, 1, 100, fd_in);
while(len > 0)
{
fwrite(arr, 1, len, fd_out);
len = fread(arr, 1, 100, fd_in);
}
fwrite(arr, 1, len, fd_out);
if(count > index)
{
printf("Completed %d round of operation of %d total rounds.\n", index, count);
fclose(fd_in);
fd_in = fopen("./audio-g711a.wav", "r");
goto rw_again;
}
fclose(fd_in);
fclose(fd_out);
return;
}
Update:
If the wav file contains a 'fact' chunk (non-PCM formats), then data chunk size offset is not 40, but 54 for example. So it better to search the 'data'-tag to calculate the data chunk offset than to use the 40 as a magic number.