GST_MESSAGE_ELEMENT Sample

main.c

#include <gst/gst.h>

static void
fakesink_handoff (GstElement* object, GstBuffer* arg0, GstPad* arg1, gpointer data)
{
	static gint cnt=0;
	GstElement *pipeline = GST_ELEMENT(data);
	(void)object;
	(void)arg0;
	(void)arg1;

	if (cnt%30 == 0) {
		gst_bus_post (
				gst_pipeline_get_bus (GST_PIPELINE (pipeline)),
		 		gst_message_new_element (
				GST_OBJECT_CAST (object), gst_structure_new ("fakesink", NULL, NULL)));
	}
	cnt++;
}

static gboolean
bus_message_handler (GstBus * bus, GstMessage * message, gpointer data)
{
	static gint handled_cnt = 0;
	GMainLoop *loop = (GMainLoop *)data;
	(void)bus;

	switch (message->type) {
		case GST_MESSAGE_ELEMENT:
			{
				handled_cnt++;
				g_message ("get message %d: %s", handled_cnt,
						gst_structure_get_name (gst_message_get_structure(message)));
				if (handled_cnt >= 3) {
					g_message ("g_main_loop_quit ()");
					g_main_loop_quit (loop);
				}
				break;
			}
		case GST_MESSAGE_EOS:
			g_message ("got EOS");
			g_main_loop_quit (loop);
			break;
		case GST_MESSAGE_WARNING:
		case GST_MESSAGE_ERROR:
			{
				GError *gerror;
				gchar *debug;

				if (message->type == GST_MESSAGE_ERROR)
					gst_message_parse_error (message, &gerror, &debug);
				else
					gst_message_parse_warning (message, &gerror, &debug);

				gst_object_default_error (GST_MESSAGE_SRC (message), gerror, debug);
				g_error_free (gerror);
				g_free (debug);
				g_main_loop_quit (loop);
				break;
			}
		default:
			break;
	}
	return TRUE;
}
int main(int argc, char *argv[])
{
	GMainLoop *loop;
	GstElement *pipeline;
	GstElement *sink;
	GstBus *bus;

	gst_init (&argc, &argv);

	loop = g_main_loop_new (NULL, FALSE);
	pipeline = gst_parse_launch ("videotestsrc ! video/x-raw,framerate=30/1 ! "
			"fakesink sync=true name=fakesink signal-handoffs=true", NULL);

	sink = gst_bin_get_by_name (GST_BIN(pipeline), "fakesink");
	g_signal_connect (sink, "handoff", G_CALLBACK(fakesink_handoff), pipeline);

	bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
	gst_bus_add_watch (bus, bus_message_handler, loop);

	gst_element_set_state (pipeline, GST_STATE_PLAYING);

	g_main_loop_run (loop);

	gst_element_set_state (pipeline, GST_STATE_NULL);
	gst_object_unref (pipeline);
	gst_object_unref (bus);

	return 0;
}

memo.md

めも

Streaming thread をトリガーとして pipeline を操作(再生/停止などを)したい場合は、 Message を使って Application thread へ伝え、Application thread から pipeline を操作するのがベター

GST_MESSAGE_ELEMENT を使った場合の実装がこのコードです。

ちなみに、Streaming thread から gst_element_set_state() や gst_element_seek() などの pipeline を操作する関数を呼ぶとデッドロックが発生します。

まとめ

pipeline に対する操作は、基本的に Application thread から行なうべき。

さんこう

キレイな実装ではないですが、同様のことは signal を使っても実装可能です。

[Application thread]
|
|                      application <----- kill(SIGUSR1) ---+
|                          |                               |
|                          v                               |
|                    signal_handler ()                     |
|                          |                               |
|                          | gst_element_seek ()           |
|                          |                               |
`------------------------- | ----------------------------- | --------
[Streaming thread]         |                               |
|                          v                               |
|                      Pipeline                            |
|                      `- filesrc ! filter !  fakesink     |
|                                                |         |
|                                                v         |
|                                             fakesink_handoff ()
|
`--------------------------------------------------------------------