Can it detect subliminal frames? Would an adequate threshold also lead to many false positives (triggering on any brutal massive change, for example a blast-inducing explosion)?
You could differentiate single-frame inserted "subliminal" (like the ones in Fight Club) images from other flashy things like explosions, by the fact that the frames right before and after the flash should be nearly identical or very similar. While after an explosion, things usually changed a bit.
This is definitely a good idea, and something that I'm most open to considering for a future release of PySceneDetect. Admittedly the current version does not handle single-frame "upsets" like this, but this does seem like a logical and reasonable approach to a first attempt at filtering them out.
I would do an exponential smoothing of pixel values over some timescale, say, 0.2 seconds, before further detection of scene changes. That should do the trick.