RTSP over HTTP probably is the wrong Remote Method. Try a different one.
Go through each and every Remote Method and use the one that works.
Change your color depth to 32bit for a performance boost
Make sure the resolution is correct, to the exact pixel. This is not always exactly the same resolution the camera's marketing material claims. Use vlc to confirm the exact resolution.
You have not told us the make and model of camera so we don't if it is Onvif compliant or not. If it is, you can skip all this and just use the Onvif probe. It will populate the parameters for you.
Every spec i've specified is the same as the cameras. I've changed to HTTP finally i've got a background-blue screen in my monitor windows and now it tells Invalid response status, Unable to get response. So i've been wrong somewhere i would like to use the probe but i'm not on camera's site and i wont be for a moment so i try everything in remote.
I tried every option as you suggested it finally worked. Just a question to make my life easier (and cause i'm also a bit lazish) is there any tutorial to learn to make an FTP server and also make my cameras uploading videos for 1 week on it ?