<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML
><HEAD
><TITLE
>Dynamic pipelines</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
REL="HOME"
TITLE="GStreamer Application Development Manual"
HREF="index.html"><LINK
REL="UP"
TITLE="Advanced GStreamer concepts"
HREF="part-advanced.html"><LINK
REL="PREVIOUS"
TITLE="Clocks in GStreamer"
HREF="chapter-clocks.html"><LINK
REL="NEXT"
TITLE="Type Detection"
HREF="chapter-typedetection.html"></HEAD
><BODY
CLASS="chapter"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
><SPAN
CLASS="application"
>GStreamer</SPAN
> Application Development Manual</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="chapter-clocks.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
></TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="chapter-typedetection.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="chapter"
><H1
><A
NAME="chapter-dynamic"
></A
>Chapter 26. Dynamic pipelines</H1
><P
>
In this chapter we will see how you can create a dynamic pipeline. A
dynamic pipeline is a pipeline that is updated or created while data
is flowing through it. We will create a partial pipeline first and add
more elements while the pipeline is playing. Dynamic pipelines cause
all sorts of scheduling issues and will remain a topic of research for
a long time in GStreamer.
</P
><P
>
We will show how to create an MPEG1 video player using dynamic pipelines.
As you have seen in the pad section, we can attach a signal to an element
when a pad is created. We will use this to create our MPEG1 player.
</P
><P
>
We'll start with a simple main function:
</P
><PRE
CLASS="programlisting"
>
/* example-begin dynamic.c */
#include <string.h>
#include <gst/gst.h>
void
eof (GstElement *src)
{
g_print ("have eos, quitting\n");
exit (0);
}
gboolean
idle_func (gpointer data)
{
gst_bin_iterate (GST_BIN (data));
return TRUE;
}
void
new_pad_created (GstElement *parse, GstPad *pad, GstElement *pipeline)
{
GstElement *decode_video = NULL;
GstElement *decode_audio, *play, *color, *show;
GstElement *audio_queue, *video_queue;
GstElement *audio_thread, *video_thread;
g_print ("***** a new pad %s was created\n", gst_pad_get_name (pad));
gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_PAUSED);
/* link to audio pad */
if (strncmp (gst_pad_get_name (pad), "audio_", 6) == 0) {
/* construct internal pipeline elements */
decode_audio = gst_element_factory_make ("mad", "decode_audio");
g_return_if_fail (decode_audio != NULL);
play = gst_element_factory_make ("osssink", "play_audio");
g_return_if_fail (play != NULL);
/* create the thread and pack stuff into it */
audio_thread = gst_thread_new ("audio_thread");
g_return_if_fail (audio_thread != NULL);
/* construct queue and link everything in the main pipeline */
audio_queue = gst_element_factory_make ("queue", "audio_queue");
g_return_if_fail (audio_queue != NULL);
gst_bin_add_many (GST_BIN (audio_thread),
audio_queue, decode_audio, play, NULL);
/* set up pad links */
gst_element_add_ghost_pad (audio_thread,
gst_element_get_pad (audio_queue, "sink"),
"sink");
gst_element_link (audio_queue, decode_audio);
gst_element_link (decode_audio, play);
gst_bin_add (GST_BIN (pipeline), audio_thread);
gst_pad_link (pad, gst_element_get_pad (audio_thread, "sink"));
/* set up thread state and kick things off */
g_print ("setting to READY state\n");
gst_element_set_state (GST_ELEMENT (audio_thread), GST_STATE_READY);
}
else if (strncmp (gst_pad_get_name (pad), "video_", 6) == 0) {
/* construct internal pipeline elements */
decode_video = gst_element_factory_make ("mpeg2dec", "decode_video");
g_return_if_fail (decode_video != NULL);
color = gst_element_factory_make ("colorspace", "color");
g_return_if_fail (color != NULL);
show = gst_element_factory_make ("xvideosink", "show");
g_return_if_fail (show != NULL);
/* construct queue and link everything in the main pipeline */
video_queue = gst_element_factory_make ("queue", "video_queue");
g_return_if_fail (video_queue != NULL);
/* create the thread and pack stuff into it */
video_thread = gst_thread_new ("video_thread");
g_return_if_fail (video_thread != NULL);
gst_bin_add_many (GST_BIN (video_thread), video_queue,
decode_video, color, show, NULL);
/* set up pad links */
gst_element_add_ghost_pad (video_thread,
gst_element_get_pad (video_queue, "sink"),
"sink");
gst_element_link (video_queue, decode_video);
gst_element_link_many (decode_video, color, show, NULL);
gst_bin_add (GST_BIN (pipeline), video_thread);
gst_pad_link (pad, gst_element_get_pad (video_thread, "sink"));
/* set up thread state and kick things off */
g_print ("setting to READY state\n");
gst_element_set_state (GST_ELEMENT (video_thread), GST_STATE_READY);
}
gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_PLAYING);
}
int
main (int argc, char *argv[])
{
GstElement *pipeline, *src, *demux;
gst_init (&argc, &argv);
pipeline = gst_pipeline_new ("pipeline");
g_return_val_if_fail (pipeline != NULL, -1);
src = gst_element_factory_make ("filesrc", "src");
g_return_val_if_fail (src != NULL, -1);
if (argc < 2)
g_error ("Please specify a video file to play !");
g_object_set (G_OBJECT (src), "location", argv[1], NULL);
demux = gst_element_factory_make ("mpegdemux", "demux");
g_return_val_if_fail (demux != NULL, -1);
gst_bin_add_many (GST_BIN (pipeline), src, demux, NULL);
g_signal_connect (G_OBJECT (demux), "new_pad",
G_CALLBACK (new_pad_created), pipeline);
g_signal_connect (G_OBJECT (src), "eos",
G_CALLBACK (eof), NULL);
gst_element_link (src, demux);
gst_element_set_state (GST_ELEMENT (pipeline), GST_STATE_PLAYING);
g_idle_add (idle_func, pipeline);
gst_main ();
return 0;
}
/* example-end dynamic.c */
</PRE
><P
> We create two elements: a file source and an MPEG demuxer.
There's nothing special about this piece of code except for
the signal 'new_pad' that we linked to the mpegdemux
element using:
</P
><PRE
CLASS="programlisting"
> g_signal_connect (G_OBJECT (demux), "new_pad",
G_CALLBACK (new_pad_created), pipeline);
</PRE
><P
>
When an elementary stream has been detected in the system stream,
mpegdemux will create a new pad that will provide the data of the
elementary stream. A function 'new_pad_created' will be called when
the pad is created.
</P
><P
> In the above example, we created new elements based on the name of
the newly created pad. We then added them to a new thread.
There are other possibilities to check the type of the pad, for
example by using the MIME type and the properties of the pad.
</P
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="chapter-clocks.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="chapter-typedetection.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Clocks in GStreamer</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="part-advanced.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Type Detection</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>
