Install Serato and the Video SL plugin. Launch the software, open the setup menu and check "Enable Video SL plugin." Close the setup menu and click the "Video" tab on the central control panel, just above the cross-fader. This will open the video window. If you have a secondary display connected (as recommended), drag the video window over to it, and click the "FullScreen" button on the control panel.
Install a screen capture application. Open the preferences and select the source for your recording. If you'd like to capture all your working of the controls, select "Capture All" or the equivalent. If you just want to capture the video output of your mix, select either your secondary display or "Output Window." Select a directory in which the captured files will be saved. Save these options by clicking "OK."
Press the "Record" button on your video capture software and begin mixing. Continue for a few seconds, then stop the recording. Use Windows Explorer to navigate to the directory of saved clips. Play the clip back to ensure it has recorded correctly.