[MEncoder-users] How to choose quality for FMP4

[Jorge Peixoto de Morais Neto]

Hi. x264 has three quality/bitrate modes: average bitrate(bitrate),
constant quantizer(qp) and constant quality(crf).
Unfortunately, FMP4 has only two modes: average bitrate (vbitrate) and
constant quantizer (vqscale). vbitrate is only good with two-pass,
unfeasible with TV capture. Constant quantizer is inefficient because
identical quantizers are used for I, P and B frames, and for complex
or simple movies.

How can I achieve in FMP4 something similar to crf?

The documentation does mention briefly that

HINT: To do constant quantizer encoding with different  quantizers
for  I/P-  and B-frames you can use: lmin=
<ip_quant>:lmax=<ip_quant>:vb_qfactor= <b_quant/ip_quant>.

Which parameters should I choose for a quality comparable to
vqscale=2? And vqscale=4?

It's hard to understand lmin and lmax with the terse documentation in
the Man page. I know
lagrange multipliers, but how do they apply to mencoder's behavior?