[FFmpeg-user] Strange CPU usage in MPEG2 encoding

[SF]

Le lundi 1 septembre 2014, 17:48:21 Roberto Ragusa a écrit :
> Something like:
> 
> valgrind --tool=callgrind --callgrind-out-file=/tmp/prof yourprogram
> 
> kcachegrind /tmp/prof

I did it and in fact all functions are consuming more, i do not see 1 function sudenly geting higher CPU needs. So no conclusion.

In fact, my problem is related to the ratecontrol for mpeg2video bitstreams. In my applicaiton, i need to
constraint the bitrate to 2.6 Mbs in 720x576, 25fps;, YUV420, in a "near CBR" mode (ie i can admit +/- 200k around this value)

Clearly, the following options : 

-b:v 2300k -maxrate 2500k -bufsize 2500k -muxrate 2500k

are consuming more than twice CPU power than 
-maxrate 2500k -bufsize 2500k -muxrate 2500k
But in this last case (ie without the -b:v), the video quality is very bad, with a lot of MB artifacts.
So : do you know a way to force mpeg2video to sustain a "near CBR" mode ? If yes, with which options (ie qmin/qmax/qscale/....?) 
Thanks for your hints, Sylvain.