GST (gstreamer) command in QMediaPlayer command - c++

Question

I am using Qt Creator 4.5.2 (Qt 5.9.5, GCC 7.3.0 64-bit) and running on Ubuntu 18.04 I am just trying to get live video stream from a IP camera. I used 'QGraphicsView', 'QGraphicsScene', 'QGraphicsVideoItem' and QMediaPlayer methods.
Right now, the video streaming source is a IP camera and I am using 'QMediaPlayer' with 'RTSP' to get the live video and it works. However, for performance and other reasons, I need to change to gstreamer type command, like 'gst-launch-1.0', to get the live video. I am having trouble to get the correct 'gst pipe' string. Need helps.
In the document for 'QMediaPlayer', it states: Since Qt 5.12.2, the url scheme gst-pipeline provides custom pipelines for the GStreamer backend.
My version is 5.9.5 so I think the GStreamer type command should work.
Related Code and comments:
// Setup GraphicsScene
mpView = ui->gvCam;
mpView->setVisible(true);
mpScene = new QGraphicsScene;
mpView->setScene(mpScene);
mpScene->setSceneRect(0, 0, mpView->width(), mpView->height());
mpView->setSceneRect(QRectF());
// Setup IP camera
mpPlayer1 = new QMediaPlayer;
mpVideoItem1 = new QGraphicsVideoItem;
mpPlayer1->setVideoOutput(mpVideoItem1);
//The following line works and I got the live stream.
mpPlayer1->setMedia(QUrl("rtsp://20.0.2.118:8554/0"));
//However, I need to use GST type command, like:
//gst-launch-1.0 rtspsrc location=rtsp://20.0.2.118:8554/0 ! decodebin ! videoscale \
! 'video/x-raw, width=480, height=270, format=I420' \
! xvimagesink sync=false force-aspect-ratio=false;
//The above GST command worked if I issued from the terminal and I got the live stream.
//But, I don't know how to put it as a 'gst pipeline' string as a parameter for 'setMedia' call.
mpScene->addItem(mpVideoItem1);
QSizeF qf1(mpView->width(), mpView->height());
mpVideoItem1->setSize(qf1);
mpVideoItem1->setAspectRatioMode(Qt::IgnoreAspectRatio);
mpPlayer1->play();

Answer 1

If your Qt version is prior to 5.12.2 then a custom pipeline won't work with QMediaPlayer, because playbin is used instead.