Hi,

I'm trying out a ffmpeg pipeline for anonymizing webcam video. One of
the filters I'd like to include is bgsubtract0r, but command line such
as the following has no perceivable effect:

    ffmpeg -i /dev/video0 -ss 1 \
        -vf "frei0r=bgsubtract0r:0.5" \
        -pix_fmt yuv420p -f xv - | ffplay -

I guess I'm expecting a solid blue background as the filter's
description states. I'm skipping the first second for the light and
aperture to turn on and open, but even increasing `threshold`
parameter all the way to 1 has no effect, so I doubt that's it.
However, other frei0r filters seem to work great!

    ffmpeg -i /dev/video0 \
        -vf "frei0r=rgbsplit0r:0.1|0.1" \
        -pix_fmt yuv420p -f xv - | ffplay -

This is ffmpeg 4.1.4 and frei0r-plugins 1.7.0.

I might be just using the filter wrong. Thanks for any clues!