[Ffmpeg-devel] DAR and SAR FFmpeg option confusion

[Michael Niedermayer]

Hi

On Tue, Mar 13, 2007 at 11:55:40AM -0700, Roman Shaposhnik wrote:
> Hi,
> 
> On Tue, 2007-03-13 at 18:36 +0000, Robert Swain wrote:
> > >    Which numbers and why do you think they are inconsistent ? Once
> > > again, please go read: http://www.mir.com/DMG/aspect.html and if 
> > > you find yourself in disagreement with what's written there then we
> > > can talk about it meaningfully. The numbers Robert and I quoted are
> > > very consistent with what's written as part of the resource mentioned
> > > above.
> > 
> > Not to put words in his mouth but I think what M?ns is getting at is that the 
> > DAR should be 15:11, not 4:3 as they claim. The video stream is 720x480 and not 
> > 704x480. If you have to set a DAR of 4:3 in the stream but the DAR should 
> > actually be 15:11, this is the lie/hack.
> > 
> > Anything using DV has to be aware of this nuance of the format if it analyses 
> > the stream, finds a DAR of 4:3 and frame dimensions of 720x480, the only way 
> > it's going to display the stream as intended is with a workaround for DV.
> 
>   I don't think its just DV, but that aside -- it seems that we've got
> three ways of solving this issue:
>   
>     * as you and M?ns pointed out admitting that the DAR is 15:11 will
>       do the trick. I guess it'll mean lots of FAQing, but that's ok
> 
>     * somehow make libavcodec aware that there's a smaller DISPLAY area
>       embedded inside the coded frame. And for that area the SAR is 
>       (obviously!) the same, but the DAR is what everybody expects it
>       to be

there is AVFrame.pan_scan to specify display areaS though i dont see how
that would affect the DAR disscussion


[...]
> 
>   Now, let me take a step back and mention that this very discussion has
> started with your post asking how one can set SAR explicitly, to which
> Michael replied that the propper way of doing it is specifying geometry
> and DAR.
> 
>   Now, given the amount of confusion it takes to figure out what the
> real DAR of the DV (and couple of other formats) frame is -- it seems
> to me that your original question still has merit. We might just need
> that way of specifying SAR explicitly after all. Don't you think ? 

ive no objections to add a command line oprion to ffmpeg to specify SAR
directly

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Concerning the gods, I have no means of knowing whether they exist or not
or of what sort they may be, because of the obscurity of the subject, and
the brevity of human life -- Protagoras
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