Lug on mkv high definition movies

Hi guys. I’m new in the forum. I have a problem with my WD TV LIVE. I have a WD Elements 1TB, HDMI, and my tv Lcd HD Ready. When i play the 720p mkv movie, the picture is not the best. I notice some lug on the motion (maybe i lose a frame). Do you know what the problem is? Any suggestions?

Thank you

Have you seen this thread?