For Google Play, YouTube was pitched by Google eventually. You cannot access your Music (Google Play Music) from YouTube uploads and no way is available to import libraries and playlists between any two services.
Yet, it is not mentioned by Google, but it is quite clear from the YouTube Music which will replace Play music in future.
To get there, YouTube does need the main injection of useful features, in that direction the same Google has taken more steps forward. Audio files are played in YouTube music via external files (file manager).
Whenever you’re browsing through an audio file, you can also opt for YouTube Music.
As per a recent report by Android Police “Still there isn’t a better way to play your external audio files within your Music App or any Google Play Music App”.
All the music files of YouTube are handled in different audio formats like WAV, MP3, and FLAC.
Reports add that feature was likely to be introduced in new Music version 3.07.52 of YouTube and currently, it’s available in 3.07.54 version.