[FFmpeg-user] Strange CPU usage in MPEG2 encoding

[SF]

Le dimanche 7 septembre 2014, 14:46:30 Roberto Ragusa a écrit :
> 
> On 09/04/2014 12:33 PM, SF wrote:
> 
> > 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
> 
> What is the resulting bitrate in the second case? Much smaller?

Yes. In the second case, the average bitrate is around 600kbs, leading to 
a very bad video quality on decoding side.

> 
> Another explanation could be that if you ask for a very
> specific bitrate the encoding process has to encode a frame,
> then retry a few times with stronger/weaker quantization to
> match the bitrate target. I suppose the code does not
> really encode, just estimate used bits, but I would not be
> surprised if estimation would be almost as slow as actual
> encoding.

I was thinking something like that also, but the same settings with mpeg4 or
x264 produces very good results (ie low CPU usage, good quality and correct
bitrates). So what's going wrong with mpeg2video ?