Ok, I found an example (I don't have snapchat installed) of one of these filters working on video (not sure if it would work for live streaming):

https://www.cnet.com/how-to/want-to-try-that-gender-face-swa...

I guess it looks...obviously like a filter, with particular distortion around the hair? In the BBC story's lede image [0], which purports to be two photos of the same vlogger, with and without the filter, her "filtered" face is substantially slimmed, yet the hair near the software-slimmed contours of the face looks, not fake at all?

[0] https://ichef.bbci.co.uk/news/660/cpsprodpb/123E0/production...