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copied!<p>Combining the comment of Artefact2 (using <code>aplay</code> for output) and the answer of kay (using <code>pipe()</code>, which I had not touched before), I came up with this "minimal" example. For the ALSA version, it creates a pipe, forks an <code>aplay</code> process with the appropriate parameters, and feeds the decoded audio to it.</p> <p>Using lots of <code>assert()</code> to show the error codes associated with the individual function calls. The next step, of course, would not be the adding of <code>-DNDEBUG</code> (which would make this program <em>really</em> quick and <em>really</em> useless), but the replacing of the asserts with appropriate error handling including human-readable error messages.</p> <pre><code>// A small example program showing how to decode an MP3 file. #include <assert.h> #include <stdlib.h> #include <mpg123.h> #include <unistd.h> #include <fcntl.h> int main( int argc, char * argv[] ) { // buffer and counter for decoded audio data size_t OUTSIZE = 65536; unsigned char outmem[OUTSIZE]; size_t outbytes; // output file descriptor int outfile; // handle, return code for mpg123 mpg123_handle * handle; int rc; // one command line parameter, being the MP3 filename assert( argc == 2 ); #ifdef OSS assert( ( outfile = open( "/dev/audio", O_WRONLY ) ) != -1 ); #else // ALSA // pipe file descriptors int piped[2]; assert( pipe( piped ) != -1 ); // fork into decoder (parent) and player (child) if ( fork() ) { // player (child) assert( dup2( piped[0], 0 ) != -1 ); // make pipe-in the new stdin assert( close( piped[1] ) == 0 ); // pipe-out, not needed assert( execlp( "aplay", "aplay", "-q", "-r44100", "-c2", "-fS16_LE", "-traw", NULL ) != -1 ); // should not return } else { // decoder (parent) close( piped[0] ); // pipe-in, not needed outfile = piped[1]; } #endif // initializing assert( mpg123_init() == MPG123_OK ); assert( atexit( mpg123_exit ) == 0 ); // setting up handle assert( ( handle = mpg123_new( NULL, NULL ) ) != NULL ); // clearing the format list, and setting the one preferred format assert( mpg123_format_none( handle ) == MPG123_OK ); assert( mpg123_format( handle, 44100, MPG123_STEREO, MPG123_ENC_SIGNED_16 ) == MPG123_OK ); // open input MP3 file assert( mpg123_open( handle, argv[1] ) == MPG123_OK ); // loop over input while ( rc != MPG123_DONE ) { rc = mpg123_read( handle, outmem, OUTSIZE, &outbytes ); assert( rc != MPG123_ERR && rc != MPG123_NEED_MORE ); assert( write( outfile, outmem, outbytes ) != -1 ); } // cleanup assert( close( outfile ) == 0 ); mpg123_delete( handle ); return EXIT_SUCCESS; } </code></pre> <p>I hope this helps others with similar problems, as a template.</p>

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