OK seems like a few folk are trying to do the same thing. A really cool ad you want to catch and share with your friends.. Right?
Hit pause to stop the ad. You can't rewind or replay it.
Right click and select Copy"Copy debug infoinfo"
Paste this into a testtext editor (or anywhere you can edit it)
Search for "ad_docid" you should find a line that reads "ad_docid": "THE ID YOU NEED",
Create the string: https://www.youtube.com/watch?v=THE ID YOU NEED
cut and paste this string into your browser
e.g. ad_docid reads "ad_docid": "zoYjXvtRkIA",
copy as https://www.youtube.com/watch?v=zoYjXvtRkIA into your browser.
Done