[FFmpeg-devel] DV Video and SAR

[Dan Dennedy]

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.

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