The complete $p$-elliptic integrals and a computation formula of $\pi_p$ for $p=4$

The complete $p$-elliptic integrals are generalizations of the complete elliptic integrals by the generalized trigonometric function $\sin_p{\theta}$ and its half-period $\pi_p$. It is shown, only for $p=4$, that the generalized $p$-elliptic integrals yield a computation formula of $\pi_p$ in terms of the arithmetic-geometric mean. This is a $\pi_p$-version of the celebrated formula of $\pi$, independently proved by Salamin and Brent in 1976.