I think what was meant was in Settings, Apps, swipe to ALL, then Media Storage. Then click the Clear Data button.
I had a similar but not identical problem on my previous phone, a GS3. Videos would show up twice, and if I deleted one, both would be gone.
The cause, in my situation, was that I was using a certain Wi-Fi file transfer app, and any videos I copied from PC to device got duplicated. Actually, they didn't get duplicated really, but the "Index Entry" for it, let's call it that for now, would be duplicated. The file was really only there once but the phone thought it was there twice. If I copied the videos over using USB, there was no index duplication. If I used a different Wi-Fi file transfer app, it wouldn't show up twice either. Only if I used this one app, would it do this.
So I cleared the Settings as described above, and then the Media Player just reindexed everything from scratch and all was okay. If I copied just one video over (as a test), sure enough, just that one video showed up twice, the rest that were there already only showed up once.
One warning, deleting the Data in Media Storage does solve this duplication issue but certain apps also use the data settings in Media Storage. Light Flow was one of those: the link between Light Flow and the Notification Sound that I was using would be lost and set to Default or silent (can't remember). The notification sound file itself was still where it always was but Light Flow could no longer "see" it (because I think it uses the Media Storage settings to point to the file). I had to set the notification sound for the app that I was setting the notification for back to what I had it set for before the reset. Not sure if ringtones and other notifications got reset also offhand.
Anyways, the deleting of the data in Media Storage should solve the issue if it's the same problem, and a possible cause of it might be the method used to transfer those songs. Let us know if that seems to apply to you or not.
