You must have noticed one thing on WhatsApp, that whenever a YouTube video is opened in this app, then it is not open in the app. Rather, you go out of WhatsApp. In which you get the help of YouTube, or browser to complete the action.
Now Whatsapp is working on a new feature in which the app is running the YouTube playback support test. This new feature has been seen in the beta version of the app. Please note that this new YouTube feature is not yet available for all users.