To connect Gstreamer with Qt in order to play a gstreamer video in the Qt Widget - qt

Question

I tried using phonon to play the video but could not succeed. Off-late came to know through the Qt forums that even the latest version of Qt does not support phonon. That's when I started using Gstreamer. Any suggestions as to how to connect the Gstreamer window with the Qt widget? My aim is to play a video using Gstreamer on the Qt widget. So how do I link the Gstreamer window and the Qt widget?
I am successful in getting the Id of the widget through winid().
Further with the help of Gregory Pakosz, I have added the below 2 lines of code in my application -
QApplication::syncX();
gst_x_overlay_set_xwindow_id(GST_X_OVERLAY(sink), widget->winId());
However am not able to link the Qt widget with the gstreamer video window.
This is what my sample code would look like :-
int main(int argc, char *argv[])
{
printf("winid=%d\n", w.winId());
gst_init (NULL,NULL);
/* create a new bin to hold the elements */
bin = gst_pipeline_new ("pipeline");
/* create a disk reader */
filesrc = gst_element_factory_make ("filesrc", "disk_source");
g_assert (filesrc);
g_object_set (G_OBJECT (filesrc), "location", "PATH_TO_THE_EXECUTABLE", NULL);
demux = gst_element_factory_make ("mpegtsdemux", "demuxer");
if (!demux) {
g_print ("could not find plugin \"mpegtsmux\"");
return -1;
}
vdecoder = gst_element_factory_make ("mpeg2dec", "decode");
if (!vdecoder) {
g_print ("could not find plugin \"mpeg2dec\"");
return -1;
}
videosink = gst_element_factory_make ("xvimagesink", "play_video");
g_assert (videosink);
/* add objects to the main pipeline */
gst_bin_add_many (GST_BIN (bin), filesrc, demux, vdecoder, videosink, NULL);
/* link the elements */
gst_element_link_many (filesrc, demux, vdecoder, videosink, NULL);
gst_element_set_state(videosink, GST_STATE_READY);
QApplication::syncX();
gst_x_overlay_set_xwindow_id(GST_X_OVERLAY(videosink), w.winId());
/* start playing */
gst_element_set_state (bin, GST_STATE_PLAYING);
}
Could you explain more in detail about the usage of gst_x_overlay_set_xwindow_id() wrt my context?
Could I get any hint as to how I can integrate gstreamer under Qt?
Please help me solve this problem.

Answer 1

I just did this same thing using python. What I had to do was connect to 'sync-message::element' on the bus and listen for a message called 'prepare-xwindow-id' (disregard the name as it works on all platforms, not just X11) sent after the video sink is setup. It sends you the sink inside that message, and that is where you pass it the window id.

Answer 2

The sample code given above will link GStreamer video window to QtWidget provided the elements are linked correctly.
filesrc should be linked to the demuxer
decoder should be linked to the filesink
Finally, the demuxer should be linked to the decoder at runtime
// link filesrc to demuxer
gst_element_link(filesrc,demux)
// link vdecoder to filesink
gst_element_link_many(vdecoder,filesink,NULL)
/*
The demuxer will be linked to the decoder dynamically.
The source pad(s) will be created at run time,
by the demuxer when it detects the amount and nature of streams.
Connect a callback function which will be executed
when the "pad-added" is emitted.
*/
g_signal_connect(demux,"pad-added",G_CALLBACK(on_pad_added),vdecoder);
// callback definition
static void on_pad_added(GstElement* element,GstPad* pad,gpointer* data)
{
GstPad* sinkpad;
GstElement * decoder = (GstElement*)data;
GstCaps* caps;
GstStructure* str;
gchar* tex;
caps = gst_pad_get_caps(pad);
str = gst_caps_get_structure(caps,0);
tex = (gchar*)gst_structure_get_name(str);
if(g_strrstr(tex,"video"))
{
sinkpad = gst_element_get_static_pad(decoder,"sink");
gst_pad_link(pad,sinkpad);
gst_object_unref(sinkpad);
}
}

Answer 3

http://cgit.freedesktop.org/gstreamer/gst-plugins-base/tree/tests/examples/overlay
has a minimal Qt example.
In your code, you should probably set the window ID before you do the state change to ready (I'm not 100% sure this is the problem though).
For playback, you should idally use the playbin2 element, something like this (completely untested):
GstElement *playbin, *videosink;
gchar *uri;
playbin = gst_element_factory_make ("playbin2", "myplaybin");
videosink = gst_element_factory_make ("xvimagesink", NULL);
g_object_set (playbin, "video-sink", videosink, NULL);
uri = g_filename_to_uri ("/path/to/file", NULL, NULL);
g_object_set (playbin, "uri", uri, NULL);
g_free (uri);
/* NOTE: at this point your main window needs to be realized,
* ie visible on the screen, and you might need to make sure
* that your widget w indeed has a 'native window' (just some
* things to check for if it doesn't work; there should be Qt
* API for this kind of thing if needed) */
QApplication::syncX();
 gst_x_overlay_set_xwindow_id(GST_X_OVERLAY(videosink), w.winId());
gst_element_set_state (playbin, GST_STATE_PLAYING);
.. check for messages like error/statechanges/tags/eos on pipeline/playbin bus

Answer 4

A project wrapping gstreamer into usable C++/Qt classes including example code:
http://code.google.com/p/qbtgstreamer/
I don't know about a direct approach, as I am not familiar with gstreamer itself.