Hi Prometeo,
How are you doing your video capture? If you are using a frame grabber then there is an example called LL Pulse Generation.vi. This example enables you to generate a pulse on your RTSI trigger line to trigger your DAQ board. You can also use your DAQ board to trigger your camera to syncronzie your data acquisition with your video capture. If you are doing your video capture using a 1394 (firewire) camera then you will have to send a trigger to the camera (not all 1394 cameras support triggering, if yours does it will have a trigger line on the camera). I hope this helps, let me know if you are doing your video capture using some other method.
Have a great day,
GG
