Diffusion of Li+ in (111) oriented thin films of the spinels Li4Ti5O12 and LiTi2O4 has been studied with Li-8 beta-detected NMR in the temperature range between 5 and 310 K. In Li4Ti5O12, the spin-lattice relaxation rate (1/T-1) versus temperature shows a clear maximum around 100 K (=T-max) which we attribute to magnetic freezing of dilute Ti3+ local magnetic moments, consistent with the results of magnetization and muon spin relaxation (mu(+) SR) measurements. The decrease in 1/T-1 with temperature above T-max indicates that Li+ starts to diffuse with a thermal activation energy (E-a) of 0.11(1) eV. In LiTi2O4, on the contrary, as temperature increases from 200 K, 1/T-1 increases monotonically up to 310 K. This suggests that Li also starts to diffuse above 200 K with Ea = 0.16(2) eV in LiTi2O4. Comparison with conventional Li-NMR on Li4Ti5O12 implies that both beta-NMR and mu(+) SR sense short-range Li motion, i.e., a jump diffusion of Li+ to the nearest neighboring sites.