The qtmultimedia-based qrreader has the concept of "strong_count":
before the scanner returns a decoded qr code result, it waits until
it has seen at least "strong_count" (e.g. 10) frames in which the qr code was seen and successfully decoded.
I think the idea might have been to reduce false positives, mis-decoding qr codes from bad frames.
However in practice it makes scanning even moderately sized qr codes really difficult for the user:
it takes several seconds (at least on my laptop cam) to obtain enough "clear" frames that count into the strong_count.
So I am lowering the strong_count to 2, down from CAMERA_FPS/3,
which makes it easier to scan, and I still haven't seen false positives even with this value.
SomberNight