Constant VP8_STATIC_THRESHOLD 

const VP8_STATIC_THRESHOLD: c_int = 100;

The squared error under which libvpx’s VP8 skips a macroblock as unchanged (its static threshold), so a still region is left as it is rather than coded again every frame: at 0.25 Mbit/s a 1080p texture under a moving box took 3.0 MB for its 3 s of motion against 5.8, at 42.0 dB against 41.4, and 304 kB still against 1185. Scrolling text codes the same.