ffmpeg will do it and you can batch it too.
md screenshot
for %%g in ("path\to\videos\*.mp4") do (path\to\ffmpeg\ffmpeg.exe -ss 15 -i "%%g" -vframes 1 -s 640x480 "screenshot\%%~ng.jpg")
that will create a screenshot folder, export a frame from the video at 15 secs at a size of 640x480 then save the image to the screenshot folder named the same as the video.
Change the size to suit etc
If you want to keep the correct aspect ratio, then use -vf scale=iw/2:ih/2:force_original_aspect_ratio=decrease:force_divisible_by=2
instead of -vframes 1 -s 640x480