Stuttering video on h264 / 720 / ACC

I just bought the latest ATV Flash (black) and recognized that videos (H-264/720/ACC) are somewhat stuttering - meaning camera movements are not smooth. When played with original Apple SW from my iTunes collection they are perfectly smooth. If I play them using uPnP/WiFi with my TV directly they are also smooth. I tried to figure out if that may be an issue of the video optimization of my TV and your video optinization but when I turned everything in my TV off it got even worse. 

Is there something I can do?