Threads
GStreamer has support for multithreading throught the use of
the GstThread object. This object is in fact
a special GstBin that will become a thread when started.
To construct a new thread you will perform something like:
GstElement *my_thread;
// create the thread object
my_thread = gst_thread_new("my_thread");
g_return_if_fail(audio_thread != NULL);
// add some plugins
gst_bin_add(GST_BIN(my_thread),GST_ELEMENT(funky_src));
gst_bin_add(GST_BIN(my_thread),GST_ELEMENT(cool_effect));
// connect the elements here...
...
// prepare the thread
gst_element_set_state(GST_ELEMENT(my_thread),GST_STATE_READY);
// start playing
gst_element_set_state(GST_ELEMENT(my_thread),GST_STATE_PLAYING);
The above program will create a thread with two elements in it. As soon
as it is set to the PLAYING state, the thread will start to iterate.
The thread must contain at least one element of type GstSrc
or GstConnection in order to work.
A thread will be visualised as below
a thread
As an example we show the helloworld program using a thread.
#include <gst/gst.h>
/* eos will be called when the src element has an end os stream */
void eos(GstSrc *src, gpointer data)
{
GstThread *thread = GST_THREAD(data);
g_print("have eos, quitting\n");
/* stop the bin */
gst_element_set_state(GST_ELEMENT(thread), GST_STATE_NULL);
gst_main_quit();
}
int main(int argc,char *argv[])
{
GstElement *disksrc, *audiosink;
GstElement *pipeline;
GstElement *thread;
if (argc != 2) {
g_print("usage: %s <filename>\n", argv[0]);
exit(-1);
}
gst_init(&argc,&argv);
/* create a new thread to hold the elements */
thread = gst_thread_new("thread");
g_assert(thread != NULL);
/* create a new bin to hold the elements */
pipeline = gst_pipeline_new("pipeline");
g_assert(pipeline != NULL);
/* create a disk reader */
disksrc = gst_elementfactory_make("disksrc", "disk_source");
g_assert(disksrc != NULL);
gtk_object_set(GTK_OBJECT(disksrc),"location", argv[1],NULL);
gtk_signal_connect(GTK_OBJECT(disksrc),"eos",
GTK_SIGNAL_FUNC(eos), thread);
/* and an audio sink */
audiosink = gst_elementfactory_make("audiosink", "play_audio");
g_assert(audiosink != NULL);
/* add objects to the main pipeline */
gst_bin_add(GST_BIN(pipeline), disksrc);
gst_bin_add(GST_BIN(pipeline), audiosink);
/* automatically setup the pipeline */
if (!gst_pipeline_autoplug(GST_PIPELINE(pipeline))) {
g_print("unable to handle stream\n");
exit(-1);
}
/* remove the source element from the pipeline */
gst_bin_remove(GST_BIN(pipeline), disksrc);
/* insert the source element in the thread, remember a thread needs at
least one source or connection element */
gst_bin_add(GST_BIN(thread), disksrc);
/* add the pipeline to the thread too */
gst_bin_add(GST_BIN(thread), GST_ELEMENT(pipeline));
/* make it ready */
gst_element_set_state(GST_ELEMENT(thread), GST_STATE_READY);
/* start playing */
gst_element_set_state(GST_ELEMENT(thread), GST_STATE_PLAYING);
/* do whatever you want here, the thread will be playing */
...
gst_main();
gst_pipeline_destroy(thread);
exit(0);
}