Hello -
Both MediaLab and DirectRT should be able to record data from a stimulant in the manner that you've thought about constructing and using.
I'm not certain - but I believe MediaLab would require quite a bit more tinkering with before you could get a system that could both record data and simultaneously play a video file. You would most likely want to rely on an external HTML page that could both play the video file and use some scripting to record actions that the user initiated while the video played. No other immediate solutions have popped into my mind; however there may be alternative methods available. A quick search of the forums may help provide more methods that others have used to conduct similar operations.
DirectRT may be easier to work with for this experiment.
If you were to take advantage of DirectRT's ability to play video files and measure continuous RT's, you could both display the video file and measure when any responses were sent from the user.
In DirectRT 2008 (and previous models) you could only take advantage of the continuous Joystick functionality; however we now have continuous Joystick, Keyboard, and Mouse RT options available in our 2010 model of the software.
I'm sure there may be more ways to complete this task; however the methods noted above are the two solutions that I can currently see as being the most optimal.
Let me know if you would like any further help - I would be glad to work with you in getting this setup.