Convert raw v4l2 buffer to QVideoframe in qt

1
votes

I will get raw video data from the V4L2 driver using VIDIOC_DQBUF, I wanted to render this frame in qt using QVideoFrame(which construct video frame) and QLabel/QPaint(for rendering a video frame).

QVideoFrame::QVideoFrame(QAbstractVideoBuffer *buffer, const QSize &size, QVideoFrame::PixelFormat format) Constructs a video frame from a buffer with the given pixel format and size in pixels. Qvideoframe from Qt

As of now, I’m using QImage to rendering RGB24 and QImage supports the only RGB format. However raw video frame which is received from VIDIOC_DQBUF is having different color formats and QVideoFrame support most of them.

Queries:

  1. How to use QVideoFrame::QVideoFrame(QAbstractVideoBuffer *buffer, const QSize &size, QVideoFrame::PixelFormat format) for v4l2 buffer ?

  2. How I can use map(), bits() and mappedBytes() function so that, I can get QVideoFrame constructed for given raw video data?

  3. How I can use QPaint/QLabel to render QVideoFrame?

Regards, Kulakrni

1
qtqpainterqlabelv4l2qtmultimedia

1 Answers

0
votes

Lets reverse the order.

How I can use QPaint/QLabel to render QVideoFrame?

You can not. You need to use a QAbstractVideoSurface() derived class. In QML, this is VideoOutput. If you want a single image, then QVideoFrame is not the correct class to use for QPaint/QLabel.

How I can use map(), bits() and mappedBytes() function so that, I can get QVideoFrame constructed for given raw video data?

These functions are your interface to the QAbstractVideoSurface. It depends on how you want to store the VL4 buffer. Are you copying/translating it or are you mapping it directly; then there are ownership issues which this API attempts to address.

How to use QVideoFrame::QVideoFrame(QAbstractVideoBuffer *buffer, const QSize &size, QVideoFrame::PixelFormat format) for v4l2 buffer

You need to sub-class a QAbstractVideoBuffer by either copying/translating the data and keeping it with the class or provide a reference if you are using zero-copy of some sort.

By default, QML Camera and QCamera will find and use /dev/videoX which is a v4l device, via GStreamer. This class should already do the right thing to supply a VideoOutput widget.

See: Qt Video overview