Information rate under fixed-length blocking
= Information rate under fixed-length blocking
For a source $(X_n)$ and fixed positive integer $N$, form the block source $Y_i=(X_{(i-1)N+1},\ldots,X_{iN})$. Whenever the original information rate $h$ exists, the blocked source has information rate $Nh$, because
$$
\frac1mH(Y_1,\ldots,Y_m)
=N\frac1{mN}H(X_1,\ldots,X_{mN}).
$$