How to stack three videos side by side with ffmpeg I'd like to combine three videos into one vertically stacked video. The three videos have different width and height.

I can combine them horizontally successfully with this command:

ffmpeg -i s1.mp4 -i s2.mp4 -i temp.mp4 -filter_complex "[1:v][0:v]scale2ref=oh*mdar:ih[1v][0v];[2:v][0v]scale2ref=oh*mdar:ih[2v][0v];[0v][1v][2v]hstack=3,scale='2*trunc(iw/2)':'2*trunc(ih/2)';[0:a:0][1:a:0][2:a:0] amix=inputs=3:duration=first:dropout_transition=0,dynaudnorm" final.mp4


How can I modify this command to stack them vertically?
For vertical stacking, the widths have to be equalized.

[1:v][0:v]scale2ref=iw:ow/mdar[1v][0v];[2:v][0v]scale2ref=iw:ow/mdar[2v][0v];[0v][1v][2v]vstack=3