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/** @file simple_client.c
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* @brief This simple client demonstrates the basic features of JACK
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* as they would be used by many applications.
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#include <jack/jack.h>
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jack_port_t *input_port;
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jack_port_t *output_port;
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jack_client_t *client;
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/* a simple state machine for this client */
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} client_state = Init;
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* The process callback for this JACK application is called in a
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* special realtime thread once for each audio cycle.
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* This client follows a simple rule: when the JACK transport is
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* running, copy the input port to the output. When it stops, exit.
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_process (jack_nframes_t nframes)
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jack_default_audio_sample_t *in, *out;
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jack_transport_state_t ts = jack_transport_query(client, NULL);
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if (ts == JackTransportRolling) {
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if (client_state == Init)
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in = jack_port_get_buffer (input_port, nframes);
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out = jack_port_get_buffer (output_port, nframes);
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sizeof (jack_default_audio_sample_t) * nframes);
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} else if (ts == JackTransportStopped) {
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if (client_state == Run)
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process (jack_nframes_t nframes, void* arg)
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jack_client_t* client = (jack_client_t*) arg;
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while ((nframes = jack_thread_wait (client, _process (nframes))) != 0);
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* JACK calls this shutdown_callback if the server ever shuts down or
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* decides to disconnect the client.
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jack_shutdown (void *arg)
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main (int argc, char *argv[])
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const char *client_name;
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const char *server_name = NULL;
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jack_options_t options = JackNullOption;
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if (argc >= 2) { /* client name specified? */
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client_name = argv[1];
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if (argc >= 3) { /* server name specified? */
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server_name = argv[2];
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options |= JackServerName;
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} else { /* use basename of argv[0] */
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client_name = strrchr(argv[0], '/');
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if (client_name == 0) {
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client_name = argv[0];
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/* open a client connection to the JACK server */
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client = jack_client_open (client_name, options, &status, server_name);
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if (client == NULL) {
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fprintf (stderr, "jack_client_open() failed, "
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"status = 0x%2.0x\n", status);
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if (status & JackServerFailed) {
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fprintf (stderr, "Unable to connect to JACK server\n");
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if (status & JackServerStarted) {
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fprintf (stderr, "JACK server started\n");
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if (status & JackNameNotUnique) {
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client_name = jack_get_client_name(client);
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fprintf (stderr, "unique name `%s' assigned\n", client_name);
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/* tell the JACK server to call `process()' whenever
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there is work to be done.
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jack_set_process_callback (client, process, client);
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/* tell the JACK server to call `jack_shutdown()' if
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it ever shuts down, either entirely, or if it
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just decides to stop calling us.
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jack_on_shutdown (client, jack_shutdown, 0);
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/* display the current sample rate.
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printf ("engine sample rate: %" PRIu32 "\n",
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jack_get_sample_rate (client));
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/* create two ports */
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input_port = jack_port_register (client, "input",
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JACK_DEFAULT_AUDIO_TYPE,
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output_port = jack_port_register (client, "output",
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JACK_DEFAULT_AUDIO_TYPE,
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JackPortIsOutput, 0);
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if ((input_port == NULL) || (output_port == NULL)) {
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fprintf(stderr, "no more JACK ports available\n");
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/* Tell the JACK server that we are ready to roll. Our
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* process() callback will start running now. */
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if (jack_activate (client)) {
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fprintf (stderr, "cannot activate client");
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/* Connect the ports. You can't do this before the client is
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* activated, because we can't make connections to clients
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* that aren't running. Note the confusing (but necessary)
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* orientation of the driver backend ports: playback ports are
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* "input" to the backend, and capture ports are "output" from
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ports = jack_get_ports (client, NULL, NULL,
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JackPortIsPhysical|JackPortIsOutput);
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fprintf(stderr, "no physical capture ports\n");
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if (jack_connect (client, ports[0], jack_port_name (input_port))) {
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fprintf (stderr, "cannot connect input ports\n");
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ports = jack_get_ports (client, NULL, NULL,
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JackPortIsPhysical|JackPortIsInput);
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fprintf(stderr, "no physical playback ports\n");
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if (jack_connect (client, jack_port_name (output_port), ports[0])) {
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fprintf (stderr, "cannot connect output ports\n");
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/* keep running until the transport stops */
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while (client_state != Exit) {
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jack_client_close (client);