Add example for replaced handle I/O.

git-svn-id: svn://scm.orgis.org/mpg123/trunk@2718 35dc7657-300d-0410-a2e5-dc2837fedb53

doc/examples/mpg123_to_wav_replaced_io.c

@@ -0,0 +1,171 @@
+/*
+	mpg123_to_wav.c
+
+	copyright 2007-2010 by the mpg123 project - free software under the terms of the LGPL 2.1
+	see COPYING and AUTHORS files in distribution or http://mpg123.org
+	initially written by Nicholas Humfrey (moved to handle I/O by Thomas Orgis)
+
+	This example program demonstrates how to use libmpg123 to decode a file to WAV (writing via libsndfile), while doing the I/O (read and seek) with custom callback functions.
+	This should cater for any situation where you have some special means to get to the data (like, mmapped files / plain buffers in memory, funky network streams).
+
+	Disregarding format negotiations, the basic synopsis is:
+
+	mpg123_init()
+	mpg123_new()
+	mpg123_replace_reader_handle()
+
+	mpg123_open_handle()
+	mpg123_read()
+	mpg123_close()
+
+	mpg123_delete()
+	mpg123_exit()
+*/
+
+#include <stdio.h>
+#include <strings.h>
+#include <mpg123.h>
+#include <sndfile.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+void usage()
+{
+	printf("Usage: mpg123_to_wav <input> <output>\n");
+	exit(99);
+}
+
+void cleanup(mpg123_handle *mh)
+{
+	/* It's really to late for error checks here;-) */
+	mpg123_close(mh);
+	mpg123_delete(mh);
+	mpg123_exit();
+}
+
+/* Simple handle for you private I/O data. */
+struct ioh { int fd; };
+
+/* The callback functions; simple wrappers over standard I/O.
+   They could be anything you like... */
+
+static ssize_t read_cb(void *handle, void *buf, size_t sz)
+{
+	ssize_t ret;
+	struct ioh *h = handle;
+	errno = 0;
+	ret = read(h->fd, buf, sz);
+	if(ret < 0) fprintf(stderr, "read error: %s\n", strerror(errno));
+
+	return ret;
+}
+
+static off_t lseek_cb(void *handle, off_t offset, int whence)
+{
+	off_t ret;
+	struct ioh *h = handle;
+	ret = lseek(h->fd, offset, whence);
+	if(ret < 0) fprintf(stderr, "seek error: %s\n", strerror(errno));
+
+	return ret;
+}
+
+/* The cleanup handler is called on mpg123_close(), it can cleanup your part of the mess... */
+void cleanup_cb(void *handle)
+{
+	struct ioh *h = handle;
+	close(h->fd);
+	h->fd = -1;
+}
+
+
+int main(int argc, char *argv[])
+{
+	SNDFILE* sndfile = NULL;
+	SF_INFO sfinfo;
+	mpg123_handle *mh = NULL;
+	unsigned char* buffer = NULL;
+	size_t buffer_size = 0;
+	size_t done = 0;
+	int  channels = 0, encoding = 0;
+	long rate = 0;
+	int  err  = MPG123_OK;
+	off_t samples = 0;
+	struct ioh *iohandle;
+
+	if (argc!=3) usage();
+	printf( "Input file: %s\n", argv[1]);
+	printf( "Output file: %s\n", argv[2]);
+
+	err = mpg123_init();
+
+	errno = 0;
+	iohandle = malloc(sizeof(struct ioh));
+	iohandle->fd = open(argv[1], O_RDONLY);
+	if(iohandle->fd < 0)
+	{
+		fprintf(stderr, "Cannot open input file (%s).\n", strerror(errno));
+		return -1;
+	}
+
+	if( err != MPG123_OK || (mh = mpg123_new(NULL, &err)) == NULL
+	    /* Let mpg123 work with the file, that excludes MPG123_NEED_MORE messages. */
+	    || mpg123_replace_reader_handle(mh, read_cb, lseek_cb, cleanup_cb) != MPG123_OK
+	    || mpg123_open_handle(mh, iohandle) != MPG123_OK
+	    /* Peek into track and get first output format. */
+	    || mpg123_getformat(mh, &rate, &channels, &encoding) != MPG123_OK )
+	{
+		fprintf( stderr, "Trouble with mpg123: %s\n",
+		         mh==NULL ? mpg123_plain_strerror(err) : mpg123_strerror(mh) );
+		cleanup(mh);
+		return -1;
+	}
+
+	if(encoding != MPG123_ENC_SIGNED_16)
+	{ /* Signed 16 is the default output format anyways; it would actually by only different if we forced it.
+	     So this check is here just for this explanation. */
+		cleanup(mh);
+		fprintf(stderr, "Bad encoding: 0x%x!\n", encoding);
+		return -2;
+	}
+	/* Ensure that this output format will not change (it could, when we allow it). */
+	mpg123_format_none(mh);
+	mpg123_format(mh, rate, channels, encoding);
+
+	/* Buffer could be almost any size here, mpg123_outblock() is just some recommendation.
+	   Important, especially for sndfile writing, is that the size is a multiple of sample size. */
+	buffer_size = mpg123_outblock( mh );
+	buffer = malloc( buffer_size );
+
+	bzero(&sfinfo, sizeof(sfinfo) );
+	sfinfo.samplerate = rate;
+	sfinfo.channels = channels;
+	sfinfo.format = SF_FORMAT_WAV|SF_FORMAT_PCM_16;
+	printf("Creating 16bit WAV with %i channels and %liHz.\n", channels, rate);
+
+	sndfile = sf_open(argv[2], SFM_WRITE, &sfinfo);
+	if(sndfile == NULL){ fprintf(stderr, "Cannot open output file!\n"); cleanup(mh); return -2; }
+
+	do
+	{
+		err = mpg123_read( mh, buffer, buffer_size, &done );
+		sf_write_short( sndfile, (short*)buffer, done/sizeof(short) );
+		samples += done/sizeof(short);
+		/* We are not in feeder mode, so MPG123_OK, MPG123_ERR and MPG123_NEW_FORMAT are the only possibilities.
+		   We do not handle a new format, MPG123_DONE is the end... so abort on anything not MPG123_OK. */
+	} while (err==MPG123_OK);
+
+	if(err != MPG123_DONE)
+	fprintf( stderr, "Warning: Decoding ended prematurely because: %s\n",
+	         err == MPG123_ERR ? mpg123_strerror(mh) : mpg123_plain_strerror(err) );
+
+	sf_close( sndfile );
+
+	samples /= channels;
+	printf("%li samples written.\n", (long)samples);
+	cleanup(mh);
+	free(iohandle);
+	return 0;
+}