[x264-devel] Re: [MOD] [PATCH] Rate control

[Laurent Aimar]

On Sun, Aug 08, 2004, Måns Rullgård wrote:
> Laurent Aimar <fenrir at via.ecp.fr> writes:
> 
> >  It seems to work pretty well :) but from my (really too) limited tests,
> > it seems to always produce lower bitrate than requested (semething like
> > 5-7%).
> 
> Which number did you look at?  The rate printed by x264_encoder_close
> is always a bit lower than the actual file size.
 The rate printed by x264_encoder_close is the rate of the slice data.
It doesn't take into account the size of PPS/SPS and the startcode added
for each nal by x264.c

>  Which of these should be the target?
The difference should be small, the overhead is < 50 bytes every IDR frame
+ 4 bytes / frame.

 Moreover it depends of the muxer, for example in .mp4 the SPS/PPS should
be store once, and there is no start code. So I think the right bitrate
is the one from x264_encoder_close.

-- 
fenrir

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