[MEncoder-users] divx v's x264

[Diogo Franco]

Em Qui, 2008-06-05 às 10:54 +1000, Alex Samad escreveu:
> On Wed, Jun 04, 2008 at 10:22:45PM +0000, J. M. wrote:
> > Alex Samad <alex <at> samad.com.au> writes:
> > 
> > > My presumption when making that statement was that I was using
> > > different codecs.  If I use different codecs then I would presume I
> > > would get different size's. 
> > 
> > Bitrate, by definition, means number of bits per unit of time (usually a 
> > second). So for example, 400 kb/s bitrate means 400 kilobits per second, which 
> > means a 60 second video takes 400*60 kilobits, i.e. 24,000 kilobits.
> > 
> > So bitrate is bitrate (and therefore filesize), regardless of the codec.
> 
> yep silly me, I thought it was something like compression ir zip v's
> rar, better algo better compression. Thus for the same source you would
> get a smaller file.
> 
> like I said silly me

You can see why H.264 performs better than almost any other codec
available today here: http://en.wikipedia.org/wiki/H.264/AVC#Features

When you use the same bitrate, you get the same filesizes. If you want
to keep the SAME QUALITY, then you'll get different filesizes. Try using
x264 with a CRF of 18 (-x264encopts crf=18) and MPEG-4 with a
fixed-quantizer of 2 (-lavcopts vqscale=2 or -xvidencopts fixed_quant=2)
and you will see the difference. The quantizer number is different
because H.264 uses a different quantizer scale, where AFAIK H.264's 18
is AVC's 2.