[Ffmpeg-devel] DAR and SAR FFmpeg option confusion

[Roman Shaposhnik]

On Tue, 2007-03-13 at 02:27 +0000, Robert Swain wrote:
> Roman Shaposhnik wrote:
> > On Tue, 2007-03-13 at 01:01 +0100, Michael Niedermayer wrote:
> >> -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.
> 
> SAR = 10/11
> 
> DAR = SAR * WIDTH/HEIGHT = (10/11) * (704/480) = 4/3
> 
> So there's nothing wrong there if it's cropped. If it isn't cropped then:
> 
> DAR = (10/11) * (720/480) = 15/11

  Well, that's the point -- if the API Michael mentioned is all we've
got, how do I specify that I need a SAR of 10:11 ? Currently, I see no
way of feeding libavcodec with DISPLAY FRAME WIDTH (704) while at the
same time having an actual ENCODED frame size being bigger (720). Again,
it could be that I'm missing something so I'd love to be educated 
(and use the knowledge to fix the DV codec once and for all).

Thanks,
Roman.