Constant HELD_REFRESH_LIMIT_S 

pub(crate) const HELD_REFRESH_LIMIT_S: f64 = 10.0;

Seconds of a constant-rate target a held refresh of the whole picture, a predicted frame, may spend before it is coded again to fit HELD_KEY_BUDGET_S where the encoder can take it back (NVENC): what a cleanup through the rate control spends at most (pipeline’s CONVERGE_S). A refresh under it stands, since coding it coarser costs the picture more than the time it saves: NVENC’s of a 1080p texture at 0.25 and 0.1 Mbit/s, 1.8 and 3.1 s of the target, came out at 1.3 and 1.7 s six to ten steps coarser, 6.4-6.8 dB worse. One of dense text at 0.1 Mbit/s at 1080p took 52 s.