How to convert OpenCV mat to NvBuffer(dmabuf_fd)

Robotics & Edge Computing Jetson & Embedded Systems Jetson Xavier NX
1

Hi,

I want to overlay a image (from a .png or .jpeg file) on video frame with gstreamer. My idea is to write a gstreamer plugin that load the image file using opencv and convert to NvBuffer(dmabuf_fd). Then I could call NvBufferComposite() to composte the video stream from gstreamer pipeline (e.g. nvv4l2camerasrc) and image together.
However, I don’t know how to convert cv::mat to NvBuffer. Or could I load the image ,decoder it to RGBA nvbuffer directly? Any help to correct this would be appreciated.

Thanks.

3

Hi,
It is supported to decode JPEG into NvBuffer. Please refer to

/usr/src/jetson_multimedia_api/samples/06_jpeg_decode

There is no hardware decoder for PNG file, you would need to use software decoder and call Raw2NvBuffer().

All NvBuffer APIs are in

/usr/src/jetson_multimedia_api/include/nvbuf_utils.h

If you use Jetpack 5, Please use NvBufSurface APIs instead of NvBuffer APIs.

4

Fine, I would try this.

Thanks

5

Sorry, i have another question if I can composite two dma fd with different pixfmt(e.g. one is YUV420M and another is I420) using NvBufferComposite().

Thanks.

6

Hi,
The format of each NvBuffer should be identical. You can convert to same format by calling NvBufferTransfom().

Per our understanding, YUV420M and I420 are NvBufferColorFormat_YUV420. It looks identical.

8

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