FFMpeg -filter_complex to place a video in a window on a larger image with text
Edited to change to additive blend.

Use

ffmpeg -loop 1 -i mic720x1280.png -i waves5.mp4 -filter_complex "color=0x000000@0,format=gbrap[bg];[0]format=gbrap,drawtext=fontfile=Montserrat-Bold.ttf: text='Hello': fontcolor=white: fontsize=44: box=1: boxcolor=black@0.5: boxborderw=10: x=(w-text_w)/2: y=100,setsar=1[img];[bg][img]scale2ref[bg][img];[bg]setsar=1[bg];[1]scale=500:-1,format=gbrap[vid];[bg][vid]overlay=70:70:format=rgb[vidbl];[vidbl][img]blend=all_mode=addition" -c:v libx264 -t 15 -pix_fmt yuv420p myvid.mp4