extract_frames.c

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/*
    extract_frams: utlize the framebyframe API and mpg123_framedata to extract the MPEG frames out of a stream (strip off anything else).
 
    This is example code only sensible to be considered in the public domain.
    Initially written by Thomas Orgis.
*/
 
#include <mpg123.h>
 
/* unistd.h is not available under MSVC, 
 io.h defines the read and write functions */
#ifndef _MSC_VER
#include <unistd.h>
#else
#include <io.h>
#endif
 
#include <stdio.h>
#include <string.h>
 
int do_work(mpg123_handle *m);
 
int main(int argc, char **argv)
{
    int ret = 0;
    mpg123_handle *m;
 
#if MPG123_API_VERSION < 46
    // Newer versions of the library don't need that anymore, but it is safe
    // to have the no-op call present for compatibility with old versions.
    mpg123_init();
#endif
    m = mpg123_new(NULL, &ret);
 
    if(m == NULL)
    {
        fprintf(stderr, "Cannot create handle: %s", mpg123_plain_strerror(ret));
    }
    else
    {
        fprintf(stderr, "I'll take your dirty MPEG audio from standard input and will write the extracted pure MPEG data to standard output.\n");
        if(argc > 1 && strcmp(argv[1], "--noinfo") == 0)
        {
            fprintf(stderr, "Enabling parsing/consuming of the Info frame so that it will not appear in output.\n");
            ret = mpg123_param(m, MPG123_REMOVE_FLAGS, MPG123_IGNORE_INFOFRAME, 0.);
        }
        else
        {
            fprintf(stderr, "If you'd have given --noinfo as argument, I would omit a LAME/Xing info frame.\n");
            ret = mpg123_param(m, MPG123_ADD_FLAGS, MPG123_IGNORE_INFOFRAME, 0.);
        }
        if(ret == 0) ret = do_work(m);
 
        if(ret != 0) fprintf(stderr, "Some error occured: %s\n", mpg123_strerror(m));
 
 
        mpg123_delete(m); /* Closes, too. */
    }
 
    return ret;
}
 
int do_work(mpg123_handle *m)
{
    int ret;
    size_t count = 0;
    ret = mpg123_open_fd(m, STDIN_FILENO);
    if(ret != MPG123_OK) return ret;
 
    ssize_t wret = 0;
    while( !wret && (ret = mpg123_framebyframe_next(m)) == MPG123_OK || ret == MPG123_NEW_FORMAT )
    {
        unsigned long header;
        unsigned char *bodydata;
        size_t bodybytes;
        if(mpg123_framedata(m, &header, &bodydata, &bodybytes) == MPG123_OK)
        {
            /* Need to extract the 4 header bytes from the native storage in the correct order. */
            unsigned char hbuf[4];
            int i;
            for(i=0; i<4; ++i) hbuf[i] = (unsigned char) ((header >> ((3-i)*8)) & 0xff);
 
            /* Now write out both header and data, fire and forget. */
            wret = write(STDOUT_FILENO, hbuf, 4);
            if(!wret)
                wret = write(STDOUT_FILENO, bodydata, bodybytes);
            fprintf(stderr, "%zu: header 0x%08lx, %zu body bytes\n", ++count, header, bodybytes);
        }
    }
 
    if(ret != MPG123_DONE)
        fprintf(stderr, "Some error occured (non-fatal?): %s\n", mpg123_strerror(m));
    if(wret)
    {
        fprintf(stderr, "Write error.\n");
        ret = MPG123_ERR;
    }
 
    fprintf(stderr, "Done with %zu MPEG frames.\n", count);
 
    return 0;
}