FFMPEG scale video according to image height when overlaying video on image

I am trying to overlay a video over an image in FFMPEG. For this I am using the below command.

-i C:\Users\Vivek\Desktop\SAM\Effects\bubbles.mp4 -i C:\Users\Vivek\Desktop\selfie.jpg -filter_complex "[1:v][0:v]scale2ref[ua][b];[ua]setsar=1,format=yuva444p,colorchannelmixer=aa=0.5[u];[b][u]overlay[v]" -map "[v]" C:\Users\Vivek\Desktop\selfie.gif

The above commands work perfectly but this stretches the image according to the video's width while I want the reverse of it i.e to stretch video to width and height of image.

Answer

Switch the inputs to the scale2ref filter.

[0:v][1:v]scale2ref[ua][b]