Blu-ray Disc™ Data Management
Data related to some Blu-ray Disc videos might be stored on the PS4™ system. You can verify the data. Select [Video Playback Settings] > [Blu-ray Disc™ Data Management].
You can delete the data from the system by pressing the OPTIONS button on the data list screen, and then selecting [Delete]. Delete some data if there is not enough free space in system storage when playing BDs.