Factorize each of the following expression:

$16 a^{4}-b^{4}$

$=\left(4 a^{2}\right)^{2}-\left(b^{2}\right)^{2}$

$=\left(4 a^{2}+b^{2}\right)\left(4 a^{2}-b^{2}\right)$

$=\left(4 a^{2}+b^{2}\right)\left[(2 a)^{2}-b^{2}\right]$

$=\left(4 a^{2}+b^{2}\right)(2 a+b)(2 a-b)$