#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "<iframe.*src=\".*embed\/(.*?)\".*?<\/iframe>"
Local $sString = "<iframe width="560" height="315" src="https://www.youtube.com/embed/ED96RtfF22E" frameborder="0 "allowfullscreen> </iframe>"
Local $sSubst = "[YT]\1[/YT]"
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