[FFmpeg-devel] DV Video and SAR

[Michael Niedermayer]

On Tue, Oct 20, 2009 at 05:40:49PM -0700, Dan Dennedy wrote:
> On Mon, Oct 19, 2009 at 11:39 AM, Baptiste Coudurier
> <baptiste.coudurier at gmail.com> wrote:
> > On 10/19/2009 11:01 AM, Charles Yates wrote:
> >>
> >> 2009/10/18 Baptiste Coudurier<baptiste.coudurier at gmail.com>
> >>
> >>> Thanks, applied.
> >>
> >>
> >> Much appreciated :-).
> >>
> >>
> >>>
> >>> This one looks ok as well. I'll apply it soon I think.
> >>>
> >>
> >> Good - thank you.
> >>
> >>
> >>>
> >>> I was wondering if we shouldn't set sar for dv to digital sar as opposed
> >>> to
> >>> analog sar considering mpeg-2 sar and how FFmpeg deals with sar in
> >>> general.
> >>> Any opinion ?
> >>>
> >>
> >> I am not sure what you mean there - to the best of my knowledge, the SAR's
> >> reported for DV and mpeg2 are (pretty much) spot on.
> >>
> >> I'll stick to 'pretty much', cos all the SD values are approximations
> >> anyway
> >> - ie: 720 * 59 / 54 != 788 (should have that, thus leaviing 10 samples on
> >> left and right which is the overscan and the central 768x576 being the
> >> true
> >> 4:3 image) - but I think they were chosen to be uniformly expressed as a
> >> pair of bytes or some similar olde worlde consideration? Is that the issue
> >> you were referring to?
> >
> > Well, the values DV SD currently uses do not follow the rule width/height ==
> > dar/sar (DV HD does). I think this is because DV doesn't use the same
> > production aperture.
> >
> > MPEG-2 does follow the rule however.
> >
> 
> I found this article on the topic to be quite interesting, which
> indicates FFmpeg's SAR values for SD DV and MPEG-2 are incorrect (and
> could be described as "swapped").
> 
> http://renomath.org/ejolson/video/aspect/
> 
> Admittedly, he did not have the resources to make enough samples, but
> what he did test was consistent.

ffmpeg implements the specifications, mpeg or otherwise, if we are buggy
in that respect, please point me to it. If not, the others are buggy.

The awnser is a little simplistic but its the way it is, if one doesnt
follow the spec one is buggy and no amount of testing different cameras
or players changes this.

[...]
-- 
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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