   DirectShow source problem
  I need a generic way of checking if a capture-device has a valid input-signal connected to it. For example, I need to be able to choose between 2 devices based on which one has a valid signal.For now I'm using an Osprey 230 and an Epiphan VGA2USB. I can check if the VGA2USB has a signal using DeviceIoControl on the device. I've noticed that the VGA2USB won't have any MediaTypes on the output-pin if there's no source signal, but that's not what the Osprey-card does. It will output a blue placeholder picture if it doesn't detect a signal.What I would really like is to do away with DeviceIoControl and be able to check for signals on a bunch of capture-devices. How is this type of thing usually done?   
  Well... Urr... I used to just check if the screen was solid blue.Hey, I was on a deadline! hehe   ;  Yeah, constantly polling the device using DeviceIoControl is the result of a previous deadline, and now another is approaching and still no 'good' solution is anywhere in sight.There has to be an interface among the 300+ that indicates signal-status, right?I can attempt to build the graph using a device that has no input-signal but it'll just give me an error at the cost of seconds (depending on the device).   