Just as the extension for search ads, Google is planning to introduce an extension for the YouTube Ads too. The use of the extension of YouTube is quite similar to the extension of search ads, it will give the users more options to take action on the ads, not only the traditional ad click. Direct users to a physical store location, submit lead generation forms, and other calls-to-actions are some of the features that the YouTube ad extension will allow the user to do.
The extension of the ad will be shown directly under the video, as you can see in the image below:

At present, the extension is only available for the TrueView in-stream and non-skippable video ads. Google has announced that the extension to add more call-to-action to the ads will be available for the 6-second bumper ad in the coming months.
As per Google, the call-to-action that is currently available for the TrueView for action ad will expand more and new features will be added in the future which, as Google claims, will drive more click and conversion for the advertisers.
Sitelink extensions are one of the call-to-action extensions that are in beta testing. Relevant links to web pages under a video ad can be added by the advertisers using this extension.
The site link extension will be available for all the TrueView for action ads in the near future and all the advertisers will be able to use the extension to get the benefits. This extension is proving to be very beneficial for the advertisers as it has resulted in 23% more conversions and 50% more clicks when it was beta tested by 30 advertisers.
Moreover, Google has announced that the site link extension will be available for all in-stream format that is bought through Google Ads. After this extension is available to use, the advertisers can select this from the extension tab in Google Ads.