FFmpeg video over video circular at specific time
Here's the filtergraph for the video portion,

[1:v]format=yuva444p,geq=lum='p(X,Y)':a='st(1,pow(min(W/2,H/2),2))+st(3,pow(X-(W/2),2)+pow(Y-(H/2),2));if(lte(ld(3),ld(1)),255,0)',split[vid][border];[border]drawbox=c=red:t=fill,geq=lum='p(X,Y)':a='st(1,min(W/2,H/2))+st(3,abs(pow(pow(X-(W/2),2)+pow(Y-(H/2),2),0.5)));if(between(ld(3),ld(1),ld(1)-10),255,0)'[border];[vid][border]overlay,scale=0.15*iw:-1,setpts=PTS-STARTPTS+2/TB[v1];[0:0][v1]overlay=W-w-20:H-h-20:eof_action=pass:enable='between(t\,2,4)'[vo1];