Constant FIRST_BAND 

const FIRST_BAND: f64 = _; // 0.015625f64

Where the encoder holds a band of the picture (EncoderQuality::band), the refresh that falls back from a constant-rate cleanup sweeps the picture a band a frame in raster order, the first FIRST_BAND of it and each next sized from the bytes of the last to BAND_BUDGETS frame budgets, so the stream keeps its rate: a whole refresh at the paint-over quantizer is 86 budgets of text at 2 Mbit/s at 1080p and queues for 240 ms on a 12 Mbit/s link.