Alright, let's get to it!
- Firstly, head over to the Youtube app settings and force stop it. You can also clear its data to avoid possible problems.
- Download/open a root browser and navigate to /data/data/com.google.android.youtube.
- Open the file called shared_prefs
- Now, open the youtube.xml in a text editor of the app you're using.
- There's a <map> element right after the <xml version>and encoding information.
Copy these lines and past them below the <map> tag.
<boolean name="exo_player_cache" value="true"/>
<boolean name="show_exo_player_debzg_messages" value="true"/>
Be sure to save the file. Then go back to Youtube app settings and force close it again to take the effect. And you're done!
A toast message "Using ExoPlayer" should appear if you attempt to play a video on YouTube. That way you'll know the ExoPlayer fully works. Buffering especially HD/FULLHD videos should be much faster than before. Feel free to leave a feedback!
Be sure to have at least youtube,xml file backup before editing system files.