I'm not sure if there's already a term for this or if its already an established technique but I was wondering if any stopmotion capture programs allow you to stream existing video footage as a semi-transparent layer over the live viewer so as to visually match the action in certain scenes?  So for example if you were making a brickfilm version of "Saving Private Ryan", it would allow you to view the original live action film in lieu of an onion skin while matching the characters movements with their lego equivalents?

My own needs are actually slightly different from the scenario I just outlined as I'm trying to animate toy wooden trains (AKA BRIO THomas etc...) to appear as much like their full scale counterparts as possible.  Thus far it looks like one of the biggest challenges in my approach is going to be matching the iconic doppler effect in the audio track of a passing train.  So in my case, instead of helping me match each frame to provide a more exact copy, a source video match feature would serve more as a point of reference.  Nevertheless I think such a feature would be just as useful for Brickfilms as for other genres.
  Does anything like this exist yet?  If so, is there a term for it?  Has anybody attempted anything similar using a stop motion capture program in tandem with a media player like VLC? 

  Thank You Very Much,