ffmpeg commands to convert gif to mp4, to rescale mp4 dimensions, to stack (vertically/horizontally) mp4s into a single video

ffmpeg commands

# convert gif to mp4
ffmpeg -i gifts.gif -movflags faststart -pix_fmt yuv420p -vf "scale=trunc(iw/2)*2:trunc(ih/2)*2" gifts.mp4

# create mp4 from images (*_value.png) in current dir
ffmpeg -framerate 2 -pattern_type glob -i '*.png' -c:v libx264 -r 30 -pix_fmt yuv420p -vf "scale=trunc(iw/2)*2:trunc(ih/2)*2" value.mp4

# create mp4 from images (*_policy.png) in current dir
ffmpeg -framerate 2 -pattern_type glob -i '*.png' -c:v libx264 -r 30 -pix_fmt yuv420p -vf "scale=trunc(iw/2)*2:trunc(ih/2)*2" policy.mp4

# create vertically stacked single video from the individual value and policy videos (they have the same width)
ffmpeg -i value.mp4 -i policy.mp4 -filter_complex "[0:v][1:v]vstack[out]" -map "[out]" out.mp4

# rescale the vertically stacked output -- since we’re going to horizontally stack out.mp4 with gifts.mp4, rescale out.mp4 so its height is 480 pixels (the height of gifts.mp4).  The -2 in “-2:480” says to set height to 480 and determine width by keeping original aspect ratio, but making it even for compatibility (with codec or something)
ffmpeg -i out.mp4 -vf scale="-2:480" out_small.mp4

# horizontally stack the two videos (first video has already been vertically stacked)
ffmpeg -i out_small.mp4 -i gifts.mp4 -filter_complex "[0:v][1:v]hstack[out]" -map "[out]" final.mp4