Query on video rendering with gstreamer and UI repaint

Sanchayan Maity

Hello,

I am using Qt 4.8 on Embedded Linux and trying to do a video/audio player with Qt for GUI and gstreamer for media playback in backend.

I have a main window with six push buttons at bottom and a QGraphicsView widget in the centre above the push buttons. I run the gstreamer pipeline and render the video to this QGraphicsScene using code as below. I had two queries.

@
QApplication::syncX();
setCentralWidget(ui->graphicsView);
gst_x_overlay_set_window_handle (GST_X_OVERLAY(video_sink), ui->graphicsView->winId());
@

I can render the video if i set the window handle to centralWidget's winId. If i set the window handle to graphicsview's window Id without doing setCentralWidget(ui->graphicsView); i can't display the video and i get a "EGL couldn't create window" error. Can someone just clarify this?
Once the video starts playing, the push buttons disappear. Something to do with the video playback but i can't figure out. I thought i will do a repaint() and update(), but it doesn't help. Can someone point me in the right direction.

I am a newbie to Qt.

I am using a Toradex Colibri T20 module and running a pipeline utilising Nvidia gstreamer elements.

@
gst-launch filesrc location=file.mp4 ! qtdemux name=demux demux.video_00 ! nv_omx_h264dec ! nv_gl_eglimagesink demux.audio_00 ! nv_omx_aacdec ! alsasink device=hw:0,0
@

This is the pipeline i am running.

SGaist

Hi and welcome to devnet,

Not the answer you are waiting but since you are using a custom pipeline you might be interested by the "QtGstreamer":http://cgit.freedesktop.org/gstreamer/qt-gstreamer/ library, it might suite your need better.

Hope it helps

andreyc

[quote author="Sanchayan Maity" date="1409142082"]

I can render the video if i set the window handle to centralWidget's winId. If i set the window handle to graphicsview's window Id without doing setCentralWidget(ui->graphicsView); i can't display the video and i get a "EGL couldn't create window" error. Can someone just clarify this?[/quote]

Without adding your widget to MainWindow or without calling show() on a widget Qt does not know what to draw. That is why you getting the error.

[quote author="Sanchayan Maity" date="1409142082"]
2. Once the video starts playing, the push buttons disappear. Something to do with the video playback but i can't figure out. I thought i will do a repaint() and update(), but it doesn't help. Can someone point me in the right direction.[/quote]

When you send winId to gstreamer it will paint the frames on a whole window. And since graphicsview is a central widget all buttons belong to the same window. So gstreamer over-paint them.

You need to create a central widget as QWidget, add buttons to the central widget and add graphicsview to the same widget lay them out using Qt layouts and then play video.

Sanchayan Maity

The graphicsview is already a part of the main window and is enabled. So calling show() is not required. Also, it's not Qt that's giving the error i believe, but, the video sink element in the gstreamer pipeline.

"When you send winId to gstreamer it will paint the frames on a whole window. And since graphicsview is a central widget all buttons belong to the same window. So gstreamer over-paint them."

I thought so, that's why i did setCentralWidget(ui->graphicsView) to only display it in garphicsview part of the mainwindow. The mainwindow has the central widget and everything is in the central widget.

With setCentralWidget(ui->graphicsView) the video is displayed only in the graphicsview window, but, still the buttons do not show once the video playback starts.