Vidireports 7: You can edit the instance.cfg (C:\Windows\System32\config\systemprofile\AppData\Roaming\VidiReports\config) file with the following url in order to add a UID manually - use "|" as a separator if you want to add more than one:

camera = usb://uid1|uid2@640x480/MJPG

VidiReports 6: Quividi doesn’t use file descriptors directly in the configuration file since the correspondence between the file descriptors and the actual physical port on the machine is not guaranteed (and is not cross-platform). Instead, VidiReports  collect the UID of the cameras connected to the system, and store the UID in the configuration file. 

If you want to set the UID manually, you can first run an instance of VidiReports and then look at the log file; you will find a section like this one below that lists available cameras and their UIDs

[] ([NFO])VidiReports  Init USB video source
[] ([NFO])VideoProducer  Webcam(s) on system:
[] ([NFO])VideoProducer     > Webcam #0 on /dev/video0 — UID: usb-0000:00:1d.7-2
[] ([NFO])VideoProducer     > Webcam #1 on /dev/video1 — UID: usb-0000:00:1d.7-1

Now copy the desired UID and set it in the local configuration file, using the webcam_uid prefix, such as in:

webcam_uid = “usb-0000:00:1d.7-2″