[FFmpeg-user] Aspect Ratios: DAR, SAR and Frame Size

Rio Kierkels riokierkels at gmail.com
Mon Jan 13 17:10:56 CET 2014

The way I think ffmpeg uses DAR and SAR on decode (and this is where I base
all my other code around ffmpeg on)
is that when you have a typical anamorphic DV source which is 720x576 on
disk but has a display aspect ratio of 16:9
it first unsqueezes the footage until the resolution reaches the DAR target
of 16:9. In this case that would be 1024x576.
Then it applies all it's magic to that frame size and on ouput if the
output display aspect ratio is equivalent of the current
frame aspect ratio it will set the DAR to 1. If it isn't it calculates what
the pixel aspect ratio has to be in order to let the
player know what transformation it has to use to get the original display
aspect ratio. I could be totally wrong here but
the code that I've written around it has not failed me yet.

And I'm sorry but I'm not sure I get the top-posting part. I just hit reply
in gmail...
This is the first mailing list I've ever participated in btw.

On 13 January 2014 16:58, Carl Eugen Hoyos <cehoyos at ag.or.at> wrote:

> Rio Kierkels <riokierkels <at> gmail.com> writes:
> > I think the ffmpeg command internally applies the SAR
> > and DAR variables and transforms the resolution until
> > SAR is 1:1 and DAR matches the resolution aspect
> > ratio when it decodes the source footage.
> I may misunderstand but this sounds (completely) wrong.
> Please avoid top-posting here.
> Carl Eugen
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