matlab报错One or more output arguments not assigned during cal

matlab报错One or more output arguments not assigned during call to'movie'
matlab语句如下
i=0
for x=0:0.1:2*pi
y=sin(x)
plot(x,y,'r*')
hold on
i=i+1;
F(i)=getframe;
end
Mo=movie(F,2);
movie2avi(Mo,'firsttime.avi','FPS',1)
运行过后会出现：
? Error using ==> movie
One or more output arguments not assigned during call to "movie".
请问这是怎么回事?该如何修改才能生成avi/
请行家解答,谢谢了!