I have an external hardrive with lots of music on it. How do I integrate that music into itunes

I would recommend the move your existing library to the external drive, e.g. by copying the iTunes folder from C:\Users\<User>\Music to D:\ (change the letter as appropriate), then press and hold down shift as you launch iTunes, select Choose Library, then browse to and open D:\iTunes\iTunes Library.itl. Next move the content that you have on the external drive into D:\iTunes\iTunes Media, and use File > Library > Add Folder to Library to import the contents of the iTunes Media folder. Any content that iTunes doesn't already know about will be added. Typically you would have the options Keep... and Copy... enabled under Edit > Preferences > Advanced such that new additions are arranged according to the metadata, e.g. music items end up at ..\iTunes Media\Music\<Album Artist>\<Album>\## <Name>.<Ext>. Turn the Keep... option off if you really want to arrange files in your own custom layout, or if you have any .wav files to import where there is data in the current paths that describes the tracks that would be lost if iTunes moved them to the usual ..\<Unknown Artist>\<Unknown Album> layout for tracks without tags. I have a script called TagFromFilename that would be useful if such were the case.

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