test $# = 1||
   exec echo usage: $0 itag-no

   sed -n '
   s/http:/https:/;
   s/m.youtube/www.youtube/;
   s/youtu.be/youtube/;
   s/embed./watch?v=/;
   #etc.;
   s/;.*//;
   w.'"$0"''
   read a < .$0;
   rm .$0;
  

  n=0;while true;do
   curl -so .$0a $a;
   unset a;
   # is tr needed probably not
   tr -cd '\12\40-\176' < .$0a \
   |exec sed '
   s/https%3A/\
   &/g;
   s/ *//; 
   /https%3A%2F%2F/!d;

   s/%3A/:/g;
   s/%2C/,/g;
   s/%2F/\//g;
   s/%3D/=/g;
   s/%3B/;/g;
   s/%3F/?/g;
   s/%26/\&/g;
   s/\\u0026/\&/g;
   s/%252C/,/g;
   s/%252F/\//g;
   s/%22/\"/g;
   s/%255B/[/g;
   s/%255D/]/g;

   ' \
   |exec sed '
   /itag='"$1"'/!d;
   #change if dont want mp4
   /video.mp4/!d;
   #change if want webm
   /webm/d;
   /ytplayer/d;
   s/;+codecs.*//;
   /timedtext/d;
   ' > .$0b;
   rm .$0a;

   read b < .$0b;
   rm .$0b;
   test ${#b} = 0||break
   #number of retries default is 10
   test $n -le 9||exit
   n=$((n+1));
  done

   exec curl -o 1.mp4 $b  
   #unset b