User specified quality for specific parts (ending, credits,
...). Each zone is
<start-frame>,<end-frame>,<option> where op-
tion may be
q=<0-51>
quantizer
b=<0.01-100.0>
bitrate multiplier
NOTE: The quantizer option is not strictly enforced. It affects
only the planning stage of ratecontrol, and is still subject to
overflow compensation and qp_min/qp_max.
