[FFmpeg-devel] Overlay documentation does not mention pixel aspect ratio.
zcybercomputing at gmail.com
Sun Nov 8 23:44:02 CET 2015
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.
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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