Showing video from camera and capture frames in the same time

[przemek]

I would like to be able to show what camera records, but also in the same time grab frames from it to perform some processing.
Right now I have two options, either:

1. Implement QAbstractVideoSurface to get the frames or
2. Use VideoWidget to show what is being recorded

How can I achieve to have both? I would like to avoid duplicating quite some complicated code from VideoWidget. I would like my QAbstractVideoSurface to draw the frames in the same efficient way as VideoWidget does. Before I just used QLabel with setting a QPixmap and the difference is noticeable.
I am aware of QVideoProbe but it doesn't work on Linux.

Maybe is there a way to pass my VideoSurface to the internals of VideoWidget, so that I can just signal the incoming frame?

I am also aware of this example:
http://doc.qt.io/qt-4.8/qt-multimedia-videowidget-example.html

Should I just use it, or is there better way to do it in qt5?

Thanks in advance.

[SGaist]

Hi and welcome to devnet,

QVideoProbe comes to mind for that.

Hope it helps

[przemek]

Yeah.... but it doesn't work. What I found is that VideoProbe and Camera only works on Android.
setSource on QVideoProbe with QCamera returns false.
So?

[SGaist]

What platform are you targeting ?

[przemek]

@SGaist Linux, Ubuntu 16.04

[przemek]

Anyone can help me here?

[SGaist]

What processing do you have in mind ?

[przemek]

I just need the frames from the video. I am using 3rd party library to recognize faces.

[SGaist]

After a quick check in the sources, it seems that the gstreamer backend provides a QMediaVideoProbeControl through the camera service, did you try to retrieve it ?

[przemek]

No. Can you guide me a little how to receive that from camera service?

[joeQ]

@przemek hi,friend,welcome

I also to learn QtMultimedia recently. and share a demonstration of a custom video widget to grab frames when play video.

you can find that in /Qt/Qt5.7.0/Examples/Qt-5.7/multimediawidgets/customvideosurface/customvideowidget

And, QVideoProbe return true on my Linux 16.04.

[SGaist]

QMediaService *QCamera::mediaService
QMediaService
Specifically the templated version of QMediaService::requestControl

[przemek]

@joeQ But does it return true when you previously called setSource to QCamera? I learned somewhere that it returns true for a video source, but for QCamera only on android.

[joeQ]

@przemek

in my Ubuntu Kylin 16.04 LTS and Qt 5.8.0

I used QVideoPlayer to play video file. it QVideoProbe::setSource can return true.

[przemek]

@SGaist I will try that, thank you.
@joeQ exactly, but when you use QCamera it doesn't work.

[przemek]

@SGaist unfrotunately this code:
qobject_cast<QMediaVideoProbeControl*>(camera.service()->requestControl("org.qt-project.qt.mediavideoprobecontrol/5.0"));
returns null :(

Maybe because I run it on Raspberry Pi?

[SGaist]

Which version of Qt are you using on your Pi ?