What's the best way to determine a demo's exact length?

I guess one option is to re-watch the demo in slowmotion with PrBoom+'s advanced HUD but that seems a little clunky.

The neatest way is to use the -levelstat command-line parameter.

I found it most convenient to automatically display the output of levelstat.txt after each recording.

Grazza said:

The neatest way is to use the -levelstat command-line parameter.

Ah, thanks! Somehow I never knew about that one.

verty said:

I found it most convenient to automatically display the output of levelstat.txt after each recording.

With batch files, I suppose? Can you post the code you use?

I won't post it here, but I've sent you a PM, Creaphis.