Re: [MEncoder-users] encoding technical question

De (from) (von) <bugfood-ml@fatooh.org> :

> Philippe MONROUX wrote:
> >> 2) Unless I am very much mistaken, CQ will not give you predictable
> >> file sizes, since it will use whatever bitrate is needed to provide
> >> the quality specified., so the basis of your question is flawed. In
> >> my experience, the only way to achieve a fixed final file size is to
> >> do two pass encoding specifying bitrate, not CQ or CR.
> >
> > Sure but, read in doc :
> >
> > resolution x CQ = (bitrate x 1000)/25 (if 25 fps)
>
> Where is this written?

Here :
http://www.mplayerhq.hu/DOCS/HTML/en/menc-feat-dvd-mpeg4.html#menc-feat-dvd-mpeg4-resolution-bitrate-compute

The ResY formula (without 16 rounding) is

ResY = SQRT( 1000*Bitrate/(25*ARc*CQ)) or

(ResY)^2 = 1000*Bitrate/(25*ARc*CQ) or

CQ*ARc*(ResY)^2 = 1000*Bitrate/25

And since ResX = ResY * ARc (without 16 rounding too) that give :

CQ*(ResX/ResY)*(ResY)^2 = 1000*Bitrate/25
CQ*ResX*ResY = 1000*Bitrate/25

Are you Ok ?

--
philippe
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