Lack of metadata is normal. IP cameras usually send MJPEG in this way, one JPEG image after another as a stream. This is the simplest MJPEG file. If you took a bunch of jpegs, put them together in a large giant file and pass it to ffmpeg, it will see it as a valid mjpeg file. Some cameras will add an extra header to contain audio data, but need not be considered a valid jpeg movement.
Many cameras will have a header, such as an X-Framerate, in the HTTP header when sending a stream, or you can set it as part of the camera configuration. However, when the camera sends only jpegs, there is no way to tell from the stream itself what the frame rate is.