[MEncoder-users] x264 lossless, or is it?

[Rich Felker]

On Mon, Dec 05, 2005 at 06:30:57PM +0100, Aleksandar Uzelac wrote:
> 
> i'm using several png files to create avi, and i want resulting avi to be pixel-exact (lossless, or is lossless something else?).
> 
> here is command line (qp_constant=0 is lossless):
> 
> mencoder "mf://*.png" -v -mf fps=0.25:type=png \
> -ovc x264 -ofps 25.000 -oac lavc \
> -lavcopts acodec=mp3:abitrate=192 \
> -x264encopts qp_constant=0 -o result.avi
> 
> input and output png file example can be found here:
> 
> http://galeb.etf.bg.ac.yu/~uzi/slike/input.png
> http://galeb.etf.bg.ac.yu/~uzi/slike/output.png
> 
> output is taken from resulting avi file with "-vo png:z=9" option.
> this is not lossless, as you can see in output.png, compared to input.png file.
> 
> or is it?

Of course it's not. You've converted an RGB image to 4:2:0-subsampled
YUV (lossy conversion), compressed _that_ image losslessly,
decompressed that image, and then converted it back to RGB (lossy).

If you want lossless compression of RGB images, use a codec that works
in RGB space without chroma subsampling.

Rich