Download video files from galaxy

The location for those videos on my is as below:

Internal storage/Android/data/com.google.android.youtube/files/Offline/(system generated folder name)/streams

There might be a minor change to this location or path on other Android devices, but all those downloaded files are saved as .exo files, in an Internal Storage of a device!

But it is also true (to the best of my knowledge) that those "offline" videos can only be played using official App, and those videos simply can not be played using any other Video/Media player application.

(means Google) controls the access to the offline file.

The permission is controlled on their server per account basis, to access those downloaded files.

There are 2 other discussions related to offline functionality here and here, which should be helpful to enrich the info about offline feature.