scale to 1024:512 and overlay

ffmpeg -f image2 -i 'input/%06d.png' -filter_complex 'scale=1024:512[vs];[vs][0:v] overlay=(main_w-overlay_w)/2:(main_h-overlay_h)/2' -f image2 'out/%06d.png'

with 1:1 sar

ffmpeg -ss 420 -i 0003_prores_deint.mov -t 42 -filter_complex '[0:v]setsar=1/1[vsar]; [vsar] scale=1024:512[vs];[vs][vsar] overlay=(main_w-overlay_w)/2:(main_h-overlay_h)/2 [over]; [over] setsar=1/1' -pix_fmt rgb24 -f image2 'overlay/%06d.png'