[maemo-developers] gstreamer on qt widget

[From: Tiago Paixao]

Hi guys,
I'm trying to get a video stream from the camera drawn on top of a qt
widget. Apparently the qt side of things is working, I'm using
XOverlays, setting the WinID of my widget, calling XSync, and all that
jazz.
Everything works fine with the "videotestsrc" from GStreamer. However,
when I switch to "v4l2camsrc" I only get a blank screen.
I suspect I'm doing something wrong in the gstreamer pipeline.
here's how I create the pipeline (borrowed from qtcartoonizer):

-------------------------------------------------------------------
#define VIDEO_SRC "v4l2camsrc"
//#define VIDEO_SRC "videotestsrc"
#define VIDEO_SINK "xvimagesink"

/* Initialize Gstreamer */

        gst_init( NULL, NULL);

	/* Create pipeline and attach a callback to its message bus */

	m_pipeline = gst_pipeline_new("test-camera");

	bus = gst_pipeline_get_bus(GST_PIPELINE(m_pipeline));
	gst_object_unref(GST_OBJECT(bus));

	/* Create elements */

	/* Camera video stream comes from a Video4Linux driver */
        camera_src = gst_element_factory_make(VIDEO_SRC, "camera_src");

        g_object_set(G_OBJECT(camera_src),"driver-name","omap3cam");
        g_object_set(G_OBJECT(camera_src),"device","/dev/video0");

	/* Colorspace filter is needed to make sure that sinks understands
the stream coming from the camera */
	csp_filter = gst_element_factory_make("ffmpegcolorspace", "csp_filter");

	/* Tee that copies the stream to multiple outputs */
	tee = gst_element_factory_make("tee", "tee");

	/* Queue creates new thread for the stream */
	screen_queue = gst_element_factory_make("queue", "screen_queue");

	/* Sink that shows the image on screen. Xephyr doesn't support XVideo
	 * extension, so it needs to use ximagesink, but the device uses
	 * xvimagesink */
	m_videoSink = gst_element_factory_make(VIDEO_SINK, "screen_sink");

	/* Creates separate thread for the stream from which the image
	 * is captured */
	image_queue = gst_element_factory_make("queue", "image_queue");

	/* Filter to convert stream to use format that the gdkpixbuf library
	 * can use */
	image_filter = gst_element_factory_make("ffmpegcolorspace", "image_filter");

	/* A dummy sink for the image stream. Goes to bitheaven */
	image_sink = gst_element_factory_make("fakesink", "image_sink");

	/* Check that elements are correctly initialized */
	if(!(m_pipeline && camera_src && m_videoSink  && screen_queue &&
csp_filter&& image_queue && image_filter && image_sink))
	{
		qDebug() << "Couldn't create pipeline elements";
		return FALSE;
	}

	/* Set image sink to emit handoff-signal before throwing away its buffer */
	g_object_set(G_OBJECT(image_sink),	"signal-handoffs", TRUE, NULL);

	/* Add elements to the pipeline. This has to be done prior to linking them */
	gst_bin_add_many(GST_BIN(m_pipeline), camera_src, csp_filter,
			tee, screen_queue, m_videoSink, image_queue,
			image_filter, image_sink, NULL);

	/* Specify what kind of video is wanted from the camera */
        caps = gst_caps_new_simple("video/x-raw-yuv",
                        "width", G_TYPE_INT, 640,
                        "height", G_TYPE_INT, 480,
			NULL);

	/* Link the camera source and colorspace filter using capabilities
	 * specified */
	if(!gst_element_link_filtered(camera_src, csp_filter, caps))
	{
		return FALSE;
	}
	gst_caps_unref(caps);

	/* Connect Colorspace Filter -> Tee -> Screen Queue -> Screen Sink *
This finalizes the initialization of the screen-part of the pipeline
*/

	if(!gst_element_link_many(csp_filter, tee, screen_queue, m_videoSink, NULL))
	{

                qDebug () << "gst video sink init fail";
		return FALSE;
	}

	/* gdkpixbuf requires 8 bits per sample which is 24 bits per* pixel */

        caps = gst_caps_new_simple("video/x-raw-rgb",
                        "width", G_TYPE_INT, 640,
                        "height", G_TYPE_INT, 480,
			"bpp", G_TYPE_INT, 24,
			"depth", G_TYPE_INT, 24,
			"framerate", GST_TYPE_FRACTION, 15, 1,
			NULL);

	/* Link the image-branch of the pipeline. The pipeline is
	 * ready after this */

	if(!gst_element_link_many(tee, image_queue, image_filter, NULL))
       {
        qDebug () << "gst tee init fail";
        return FALSE;
    }

	if(!gst_element_link_filtered(image_filter, image_sink, caps))
    {
        qDebug () << "gst filterinit fail";
        return FALSE;
    }

    gst_caps_unref(caps);
    gst_element_set_state(m_pipeline, GST_STATE_NULL);
    qDebug () << "gst init ok";
    return TRUE;
-------------------------------------------------------------------

Any ideas? please?

Tiago