Set ffmpeg capture properties with cv::VideoCapture

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With the last versions of OpenCV compiled with ffmpeg.

How do I set ffmpeg capture properties with cv::VideoCapture?

I know there is the method bool VideoCapture::set(int propId, double value); But there are no "propId" for ffmpeg.

I am particularly interested in forcing ffmpeg to use TCP/IP instead of UDP when using RTSP.

I know ffmpeg allow it. For example : av_dict_set(&opts, "rtsp_transport", "tcp", 0);

Thank you