$ ffmpeg -v error -f lavfi -i testsrc=d=1 out%02d.png
$ ffprobe -v error -show_entries stream=width,height out01.png
[STREAM]
width=320
height=240
[/STREAM]
$ ffmpeg -v error -f image2 -pattern_type glob -i 'out*.png' -r 12 -s 640x480 foo.avi
$ ffprobe -v error -show_entries stream=width,height out01.png
[STREAM]
width=320
height=240
[/STREAM]