#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?m)<a [^>]*href="https://www\.youtube\.com/watch\?v=([^"&]+)[^>]*>(?s:.*?)</a>"
Local $sString = "" & @CRLF & _
"<a target="_blank" href="https://www.youtube.com/watch?v=pahhmV4WUUU" >" & @CRLF & _
"</a>" & @CRLF & _
"" & @CRLF & _
""
Local $sSubst = "<iframe width="560" height="315" src="https://www.youtube.com/embed/$1" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" 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