This is difficult right now, because we are treating the input file as a stream right now. So the data input is just a continuous stream of data, which eventually reaches EOF. This streaming allows some cool features in future: e.g. you could record your data on a low power laptop, and stream it over the network to a powerful computer that does all the calculations.
We could write a special case when streaming for a file to get a progress bar, this should not be too difficult.