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A VERY SIMPLE EXAMPLE

Copy audio signal from an input to an output

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

#include <jack/jack.h>

jack_port_t *input_port;
jack_port_t *output_port;

int
process (jack_nframes_t nframes, void *arg)

{
	jack_default_audio_sample_t *out = (jack_default_audio_sample_t *) jack_port_get_buffer (output_port, nframes);
	jack_default_audio_sample_t *in = (jack_default_audio_sample_t *) jack_port_get_buffer (input_port, nframes);

	memcpy (out, in, sizeof (jack_default_audio_sample_t) * nframes);

	return 0;      
}

int
main (int argc, char *argv[])
{
	jack_client_t *client;
	const char **ports;

	if (argc < 2) {
		fprintf (stderr, "usage: jack_simple_client <name>\n");
		return 1;
	}

	/* try to become a client of the JACK server */

	if ((client = jack_client_new (argv[1])) == 0) {
		fprintf (stderr, "jack server not running?\n");
		return 1;
	}

	/* tell the JACK server to call `process()' whenever
	   there is work to be done.
	*/

	jack_set_process_callback (client, process, 0);

	/* create two ports */

	input_port = jack_port_register (client, "input", JACK_DEFAULT_AUDIO_TYPE, JackPortIsInput, 0);
	output_port = jack_port_register (client, "output", JACK_DEFAULT_AUDIO_TYPE, JackPortIsOutput, 0);

	/* tell the JACK server that we are ready to roll */

	if (jack_activate (client)) {
		fprintf (stderr, "cannot activate client");
		return 1;
	}

	/* connect the ports. Note: you can't do this before the
	   client is activated, because we can't allow connections to
	   be made to clients that aren't running.

	   we want to connect to the first two "physical" input &
	   output ports, which will likely be the first two channels
	   of an audio interface (if there is one).
	*/

	if ((ports = jack_get_ports (client, NULL, NULL, JackPortIsPhysical|JackPortIsOutput)) == NULL) {
		fprintf(stderr, "Cannot find any physical capture ports");
		exit(1);
	}

	if (jack_connect (client, ports[0], jack_port_name (input_port))) {
		fprintf (stderr, "cannot connect input ports\n");
	}

	free (ports);
	
	if ((ports = jack_get_ports (client, NULL, NULL, JackPortIsPhysical|JackPortIsInput)) == NULL) {
		fprintf(stderr, "Cannot find any physical playback ports");
		exit(1);
	}

	if (jack_connect (client, jack_port_name (output_port), ports[0])) {
		fprintf (stderr, "cannot connect output ports\n");
	}

	free (ports);

	/* Since this is just a toy, run for a few seconds, then finish */

	sleep (10);
	jack_client_close (client);
	exit (0);
}