Create 2 instances of the TVideoGrabber component, one for the preview and one for the recording, e.g.:

VideoGrabberPreview.VideoSource = vs_IPCamera
VideoGrabberPreview.IPCameraURL = "rtsp://..." or "onvif://..." // low res D1/CIF rtsp URL
VideoGrabberPreview.StartPreview()

VideoGrabberRecording.VideoSource = vs_IPCamera
VideoGrabberRecording.IPCameraURL = "rtsp://..." or "onvif://..." // HD stream URL
VideoGrabberRecording.FrameGrabber = fg_Disabled
VideoGrabberRecording.VideoRenderer = vr_None // no rendering
VideoGrabberRecording.StartRecording()

– if using rtsp://… URL syntaxes, look at the user manual of the IP camera to determine the HD stream and low res stream URL syntaxes

– if using onvif:// URL syntaxes, the stream can be selected by its index in the [0..n-1] range by adding the index at the end of the URL, e.g.:
. onvif//user:password@192.168.1.34/0 // selects the HD stream
. onvif//user:password@192.168.1.34/1 // selects the low res stream