[Ffmpeg-devel] DAR and SAR FFmpeg option confusion

[Roman Shaposhnik]

On Tue, 2007-03-13 at 02:41 +0000, Robert Swain wrote:
> >   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).
> 
> That's the point, the SAR of 10:11 is correct for the 704x480 pixels to be 
> displayed with an aspect ratio of 4:3. But you have 720x480 pixels, so you 
> assume the SAR of 10:11 (because the sample aspect ratio is constant through any 
> cropping/padding process, which is basically what is happening as you're padding 
> 8 extra pixels to the left and right of the frames) and calculate your DAR from 
> that, which is 15:11. Try your NTSC 4:3 DV stream that is 720x280 with -aspect 
> 15:11.

  I see your point now and it does make sense. That said, I guess
my biggest concern would be that starting to demand DAR being 15:11 
for 4:3 DV (or anything else for that matter) might be problematic from
a usability standpoint plus it might present a problem as far as
flagging 4:3 in various containers is concerned.

  But I guess, if admitting DAR being 15:9 instead of 4:3 is our 
official "party line" I would protest too loudly ;-)  

Thanks,
Roman. 

P.S. But then, again:
  $ ffmpeg -h | grep aspect
     -aspect aspect      set aspect ratio (4:3, 16:9 or 1.3333, 1.7777)