#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?m)(youtu.*be.*)\/(watch\?v=|embed\/|v|shorts|)(.*?((?=[&#?])))"
Local $sString = "<p>http://www.youtube.com/watch?v=0zM3nApSvMg&feature=feedrec_grec_index <br><br>https://youtube.com/shorts/0dPkkQeRwTI</p><h2>Para</h2>" & @CRLF & _
"<p>http://www.youtube.com/user/IngridMichaelsonVEVO#p/a/u/1/QdK8U-VIH_o</p><p>Para</p>" & @CRLF & _
"<p>http://www.youtube.com/v/0zM3nApSvMg?fs=1&hl=en_US&rel=0</p><p>Para</p>" & @CRLF & _
"<p><br>http://www.youtube.com/watch?v=0zM3nApSvMg#t=0m10s</p><p>Para</p>" & @CRLF & _
"<p>Check out my youtube video: http://www.youtube.com/embed/0zM3nApSvMg?rel=0</p><p>Para</p>" & @CRLF & _
"<p>http://www.youtube.com/watch?v=0zM3nApSvMg</p><p>Para</p>" & @CRLF & _
"<p><br>http://youtu.be/0zM3nApSvMg</p><p>Para</p>" & @CRLF & _
"<div>https://youtube.com/shorts/0dPkkQeRwTI?feature=share</div>" & @CRLF & _
"<p>https://youtube.com/shorts/0dPkkQeRwTI</p><p>Para</p>" & @CRLF & _
"<p>https://www.youtube.com/watch?v=0dPkkQeRwTI&ab_channel=RelaxedChan</p><p>Para</p>"
Local $sSubst = "<iframe width="100%" src="https://www.youtube.com/embed/$3" frameborder="0" allowfullscreen></iframe>"
Local $sResult = StringRegExpReplace($sString, $sRegex, $sSubst)
MsgBox($MB_SYSTEMMODAL, "Result", $sResult)
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for AutoIt, please visit: https://www.autoitscript.com/autoit3/docs/functions/StringRegExp.htm