Thread: Play sound on a Mac

>>> Split from C program to play a sound - please don't dig up old posts, see the rules >>>

Originally Posted by MK27

DWK was right about my invocation of "execvp" being wrong -- hopefully i'm about to correct myself.

If your problem with using "system" or "exec" is that you can't stop playback after it's started, then I have your solution (I once made a perl/Tk mp3 app where this figured in). Linux uses process id's ("pid"s) to track all running processes (see a list with "ps"), and you can signal the mp3 playing process to do different things with it's pid.

If you use a simple console based app like mpg123, you can call it without any pop-up windows popping up, etc -- it just plays the file. Then get the pid and kill it when you want. In perl "system" forks a process automatically and returns you the new pid (easy). In C, running a separate program with "system" and "exec" does NOT give you a new pid -- so if you kill the "mpg123" process you will kill your entire program. So you have to fork a process (=what I learned about C today).

Anyway, the following code will play a song until you hit ENTER, then it kills mpg123 (stopping the playback) and leaves a message.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h> // for execlp

int main () {
        pid_t x;      // a special kind of int
        char kil[20] = "kill -s 9 ";

        x = fork();   /* now there's actually two "x"s:
if fork succeeds, "x" to the CHILD PROCESS is the return value of fork (0)
and "x" to the PARENT PROCESS is the actual system pid of the child process.*/
        
        if (x < 0) {  // just in case fork fails 
                puts("fork failure");
                exit(-1);
        }   
        else if (x == 0) { // therefore this block will be the child process 
                execlp("mpg123", "mpg123", "-q", "/songs/bertha.mp3", 0); 
        }                   // see GNU docs, "system" also works                
        else {  printf("from parent: mpg123 is pid %d\nENTER to quit\n", x);
                sprintf(kil,"%s%d",kil,x);
                getchar();  // wait for user input
                system(kil);
                printf("All ");
        }       /* witness that the "else if" and "else" blocks are both executed here in parallel. The "else" 
   (parent) block is continuous with the rest of the program (since the PARENT PROCESS is actually
   the program itself) so... */
        printf("done.\n");
        exit(0);
}

Get it? Anyway, that might be all you need.

Hi,

I wanna use the above code to play *.mp3. I replaced the filename "/songs/bertha.mp3" by a filename i want to play on. i complied and run it with the following command

gcc *.c
then

./a.out


i am getting the following

from parent: mpg123 is pid 9832
ENTER to quit
done.


It doesn't play the mp3. It seams that i missed something. Can you help me?


Thanks,

Joealem.

P.S : I am working on mac.

Nor do I.