[Ffmpeg-devel] DAR and SAR FFmpeg option confusion

Roman Shaposhnik rvs
Tue Mar 13 03:06:22 CET 2007


Hi

On Tue, 2007-03-13 at 01:01 +0100, Michael Niedermayer wrote:
> > > I haven't done any print debugging but looking at the SAR reported by x264, 
> > > these values are not affected by -vaspect, grepping for vaspect in the code 
> > > returns no results and it isn't documented anywhere yet ffmpeg doesn't report 
> > > any unrecognised option error. :/
> > 
> >   I have the same issue with DV (not being able to use SAR for real) so
> > if you ever figure this out -- there'll be at least two clients for the
> > functionality.
> 
> -aspect should set DAR, DAR + width and height -> SAR if this doesnt work
> its a bug

  Well, here's the problem DV has (and please let me know if I'm missing
something or if the solution is obvious). Lets take NTSC 4:3 DV as an
example here (just to talk in numbers as opposed to variables):

   1. FRAME WIDTH == [width in the quote above] == 720
      DISPLAY FRAME HEIGTH == FRAME HEIGHT == 
                     [height in the quote above] == 480 
   
   2. DISPLAY FRAME WIDTH == 704

   3. DAR == 4:3

  Now, given your formula, the SAR will be calculated as being 8:9
  where the correct one is 10:11.

As usual, http://www.mir.com/DMG/aspect.html provides more details.

Thanks,
Roman.
   
     





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