Different number of frames importing .wmv versus .avi

When I import a video in the format of .wmv I have 4000 less frames than when I import the same video in the .avi format (54000 frames).

The video is the same time length and therefore I would believe to have the same number of frames considering it's a set time length and frame rate.

When importing to MATLAB is it common to lose frames from a .wmv?