Streaming the output of openCV real-time as an RTSP stream with ffmpeg

I receive an RTSP video stream from an IP camera into my OpenCV program, which I then process for pedestrian detection; I now want to send the video comprising of bounding boxes around people detected as an rtsp stream over the network.

I am trying to use ffmpeg to do this; I can write the video using OpenCV video writer and also stream video file using ffmpeg as an rtsp stream, but I am unable to do both of this simultaneously so that it is real-time.

Most search results talk about how to receive an RTSP stream into OpenCV and I have not found much help in this regard.