  We study the transition form factors between pseudoscalar and vector mesons
using a covariant fermion field theory model in $(3+1)$ dimensions. Performing
the light-front calculation in the $q^+ =0$ frame in parallel with the
manifestly covariant calculation, we note that the suspected nonvanishing
zero-mode contribution to the light-front current $J^+$ does not exist in our
analysis of transition form factors. We also perform the light-front
calculation in a purely longitudinal $q^+ > 0$ frame and confirm that the form
factors obtained directly from the timelike region are identical to the ones
obtained by the analytic continuation from the spacelike region. Our results
for the $B \to D^* l \nu_l$ decay process satisfy the constraints on the
heavy-to-heavy semileptonic decays imposed by the flavor independence in the
heavy quark limit.
