如图,已知椭圆\(C:\; \dfrac {x^{2}}{a^{2}}+ \dfrac {y^{2}}{b^{2}}=1(a > b > 0)\)与直线\(l\):\(y= \dfrac {1}{2}x+1\)交于\(A\)、\(B\)两点.
\((1)\)若椭圆的离心率为\( \dfrac { \sqrt {2}}{2}\),\(B\)点坐标为\((- \dfrac {4}{3}, \dfrac {1}{3})\),求椭圆的标准方程;
\((2)\)若直线\(OA\)、\(OB\)的斜率分别为\(k_{1}\)、\(k_{2}\),且\(k_{1}k_{2}=- \dfrac {1}{4}\),求证:椭圆恒过定点,并求出所有定点坐标.