ffmpegで連番画像を動画にするとき、連番の範囲を指定する方法

generate.rb

command = "ffmpeg -f image2 -r 60 -start_number  1 -i img%05d.png -vframes 10 -r 60 -an -vcodec libx264 -y -pix_fmt yuv420p frame_video1.mp4"
system(command)

command = "ffmpeg -f image2 -r 60 -start_number 11 -i img%05d.png -vframes 10 -r 60 -an -vcodec libx264 -y -pix_fmt yuv420p frame_video2.mp4"
system(command)

command = "ffmpeg -f image2 -r 60 -start_number 21 -i img%05d.png -vframes 10 -r 60 -an -vcodec libx264 -y -pix_fmt yuv420p frame_video3.mp4"
system(command)