You can think of this as a time-varying signal f(t) that is sampled 30 times a second.

To add on @yirenng 's comment, each time this signal f(t) is sampled, it is actually sampled as the avarage within a 1/800 s window: $\frac{1}{800}\int_{t_0}^{t_0 + 1/800} f(t) dt$.