I followed the Youtube tutorial by Mikey Cal Meyers on how to blur out an object in a strip. (All of his others have been so excellent). I followed his instructions to the tee, built the mask, got it all keyframed perfectly against my raw, never-cut strip. Then when I reviewed the mask playback over the video, it jumped all over the place, and did not follow the mask keyframes playing alongside in the identical video in the mask window. I went back and redid the steps from the tutorial, and got the same undesirable result.
I am running Blender 2.77 on a 64-bit laptop running Windows 8.
Anyone have experience overcoming this hurdle?