[Ffmpeg-devel] [RFC] ratecontrol buffer size magic

[Måns Rullgård]

Baptiste Coudurier <baptiste.coudurier at smartjog.com> writes:

> Hi,
>
> I stumbed accross a weird behaviour of the CBR ratecontrol lately,
> basically doing:
>
>  ffmpeg -i file.mpg -vcodec mpeg2video -minrate 30000k -maxrate 30000k
> -b 30000k -intra -flags +ildct+low_delay -dc 10 -flags2
> +ivlc+non_linear_q -ps 1 -qmin 1 -qmax 12 -top 1 -vglobal 4 -acodec
> pcm_s16be -f mov -bufsize 1200000 -rc_init_occupancy 1200000 cbr.mov
>
> Constraints are so in order to achieve vbv delay as 3600.
> Now ffmpeg will only give me qp as 24. While tweaking I changed some
> magic in ratecontrol.c (see patch attached) and now qp have decent/good
> values.

In general, you cannot mix bitrate and quantizer constraints.  They
are interdependent, so an arbitrary combination may well be impossible
to achieve.

-- 
M?ns Rullg?rd
mru at inprovide.com