Analog cameras are often connected to Network Video Recorders (NVRs) that support H.264 RTSP streams served from the NVR itself. So the easiest way to connect those analog cameras to Camio is to obtain the video stream from the NVR rather than from the camera.
If your NVR doesn't support H.264 RTSP streams either, then you'll need to use a video encoder to convert the analog video into digital H.264.
For example, Axis has an overview of its encoders at https://www.axis.com/files/whitepaper/wp_encoders_73357_en_1906_hi.pdf
You'll find encoders that can handle 1, 4 or many streams with encoders like: