[FFmpeg-devel] Overlay documentation does not mention pixel aspect ratio.

Michael Niedermayer michael at niedermayer.cc
Mon Nov 9 22:59:26 CET 2015

On Sun, Nov 08, 2015 at 02:44:02PM -0800, Zach Swena wrote:
> Hi,
> I would like to propose a change to the documentation for the overlay
> filter.  The overlay filter does not detect pixel aspect ratio.  This
> causes improper display resolution when overlaying smaller images on a
> larger image.  A common example of this would be overlaying an SD source on
> an HD one.  The documentation does not mention the fact that overlay
> ignores pixel aspect ratio because it is a pixel by pixel operation.  It
> would be nice to remind people that they need to overlay pictures with the
> same pixel aspect ratio or perform a scaling operation.  One common example
> of this would be overlaying SD video on a HD background.  I tried to make a
> patch, but I couldn't find the right file.
> It would be nice to add something like this at the end of the 9.83 section
> just prior to section 9.83.1 in what becomes ffmpeg-filters.html.  Please
> let me know if I need to submit this in some other form.

a git patch for doc/filters.texi would be ideal

> Please note that overlay is a pixel per pixel operation so a scaling
> operation will be required to properly combine sources with different
> source aspect ratios such as SD and HD video.
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

What does censorship reveal? It reveals fear. -- Julian Assange
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