\[ \boxed { {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) ={\frac { \left ( -256\,a{x}^{2}y \left ( x \right ) -32\,{a}^{2}{x}^{6}-256\,a{x}^{2}+512\, \left ( y \left ( x \right ) \right ) ^{3}+192\,{x}^{4}a \left ( y \left ( x \right ) \right ) ^{2}+24\,y \left ( x \right ) {a}^{2}{x}^{8}+{a}^{3}{x}^{12} \right ) x}{512\,y \left ( x \right ) +64\,a{x}^{4}+512}}=0} \]
Mathematica: cpu = 0.022503 (sec), leaf count = 81 \[ \left \{\left \{y(x)\to \frac {1}{8} \left (-a x^4-8\right )+\frac {1}{512 \left (\frac {1}{512}-\frac {1}{\sqrt {c_1-262144 x^2}}\right )}\right \},\left \{y(x)\to \frac {1}{8} \left (-a x^4-8\right )+\frac {1}{512 \left (\frac {1}{\sqrt {c_1-262144 x^2}}+\frac {1}{512}\right )}\right \}\right \} \]
Maple: cpu = 0.047 (sec), leaf count = 80 \[ \left \{ y \left ( x \right ) =-{\frac {1}{8} \left ( \sqrt {-{x}^{2}+{ \it \_C1}}a{x}^{4}-a{x}^{4}-8 \right ) \left ( -1+\sqrt {-{x}^{2}+{\it \_C1}} \right ) ^{-1}},y \left ( x \right ) =-{\frac {1}{8} \left ( \sqrt {-{x}^{2}+{\it \_C1}}a{x}^{4}+a{x}^{4}+8 \right ) \left ( 1+\sqrt {-{x} ^{2}+{\it \_C1}} \right ) ^{-1}} \right \} \]