Add YouTube video as resource to product
go to YouTube and grab video Embed code. YouTube generate it for you in the Share Tab
Add video embed code to your product using Resource Library in Media Tab. Make sure to select 'video' resource type, see screenshot
Create Data Listing Block with Media and enable it in default products layout.
* To create block go to Admin → Design → Blocks. Use Data Listing Block type. Make sure to select Listing Data Source: Media and Media Type: Video
Go to Admin → Design → Layout select Default Product Page layout and enable video block