ffmpeg -framerate 9 -i frame%04d.png -c:v libx264 -pix_fmt yuv420p out_4.mp4 ffmpeg -framerate 9 -i "frame (%d).png" -c:v libx264 -pix_fmt yuv420p out_4.mp4 ffmpeg -i out_3.mp4 -i out_4_test.mp4 -filter_complex hstack 34merged.mp4