escapeFilterValue

The one escaping function every typed filter argument passes through (KD-1).

FFmpeg's filter description syntax gives \, ', :, ,, ;, [, ] and = structural meaning. A value containing any of them (or whitespace, which the parser trims) is escaped the way FFmpeg's own docs prescribe: backslash-escape \ and ', then wrap the whole value in single quotes. A plain value passes through untouched so the compiled strings stay readable, which law 4 (values, not magic) cares about: the compiled description is what a bug report carries.