Many motions lead to drastic degradation of QoS in multimedia communications. However, previous scheduling schemes do not consider the effect of motions in video streaming. Here we highlight the importance of handling motions and introduce a new kind of attack manipulating the amount of motions, called Motion based DoS (MDoS) attacks. And, we propose a dynamic multimedia scheduling scheme against MDoS attacks, called Scheduling Multimedia against MDoS attacks (SMaM). SMaM dynamically schedules video streams adaptive to the current network conditions. Specifically, SMaM increases resilience against MDoS attacks coping with motion traffic. Experimental results show that SMaM maximizes video quality regardless of the change in the amount of motions. Especially, SMaM minimizes the amount of useless frames for dynamically changing video, e.g. 45 % improvement over conventional scheduling schemes, which we call preferential packet scheduling (PPS). Also, SMaM presents low and stable average delay, which shows 16 % improvement over PPS schemes.