gstreamer and qt interaction

[pfarmer]

On 03/09/2013 03:01 AM, Mcnv [via GStreamer-devel] wrote:
> Hi,
> I have written a small application for playing a audio/video file in 
> Gstreamer.
> now i want to display or redirect video/audio content to a specific 
> window of Qt instead of launching a player window.
>
> request help on this.
>
>
>
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You can use QtGStreamer 
(http://gstreamer.freedesktop.org/data/doc/gstreamer/head/qt-gstreamer/html/). 

For another way there is an example in the  gstvideooverlay 
documentation 
(http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-base-libs/html/gst-plugins-base-libs-gstvideooverlay.html)
Or you can use gst_app_sink. With gstreamer-1.0 and Linux:
If you have a Capture class with a pipeline with an appsink a callback 
can be registered

GstElement* sink;
sink = gst_bin_get_by_name(GST_BIN(m_pipeline), "sink");
     gst_app_sink_set_emit_signals(GST_APP_SINK(sink), TRUE);
     g_signal_connect(sink, "new-sample", G_CALLBACK(newSample), 
(gpointer)this);
     gst_element_set_state(m_pipeline, GST_STATE_PLAYING);

This callback may look like this:

GstFlowReturn Capture::newSample(GstAppSink* sink, gpointer gSelf)
{
     GstSample* sample = NULL;
     GstBuffer* sampleBuffer = NULL;
     GstMapInfo bufferInfo;

     Capture* self = static_cast<Capture* >(gSelf);
     sample = gst_app_sink_pull_sample(GST_APP_SINK(sink));
     if(sample != NULL)
     {
         sampleBuffer = gst_sample_get_buffer(sample);
         if(sampleBuffer != NULL)
         {
             gst_buffer_map(sampleBuffer, &bufferInfo, GST_MAP_READ);
             self->m_mutex.lock();
             self->m_image = QImage(bufferInfo.data, 320, 180, 
QImage::Format_RGB888);
             self->m_mutex.unlock();
             gst_buffer_unmap(sampleBuffer, &bufferInfo);
         }
         gst_sample_unref(sample);
     }
     return GST_FLOW_OK;
}

The m_imgae can be returned with:

QImage Capture::getFrame()
{
     QMutexLocker locker(&m_mutex);
     return m_image;
}

With the private member variables of Capture
QImage m_image;
QMutex m_mutex;

The image can be displayed with e.g. a QLabel. With a subclassed QLabel 
the image from the Capture can be continuously retrieved:

Display::Display(QWidget* parent) :
     QLabel(parent),
     m_capture(new Capture(this))
{
}

void Display::paintEvent(QPaintEvent* paintEvent)
{
     setPixmap(QPixmap::fromImage(m_capture->getFrame()));
     QLabel::paintEvent(paintEvent);
}




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