This article shows you how to scale image in a dirctory with ffmpeg and conserve the aspect ratio.
Because ffmpeg is a video management tool, it can also modify a frame, in other word, an image.
In this tutorial, we create image of 1920 width. Therefore we create a new directory called 1920.
REM cd /directory/where/you/have/your/images
mkdir 1920
Test with one image if your transformation parameters give the expected result.
For example, in this case, we scale the image down to 1920 pixles
ffmpeg -i input.jpg -vf scale=1920:-1 1920/input.png
In your favorite shell, use the loop structure and call the ffmpeg command
Example:
for %v in (*.jpg) do ffmpeg -i %v -vf scale=1920:-1 1920/%v