About cached files in "Other"
iTunes categorizes cached music, videos, and photos as Other instead of actual songs, videos, or photos. Cached files are created when you stream or view content like music, videos, and photos. When you stream music or video, that content is stored as cached files on your iOS device so you can quickly access it again.
Your iOS device automatically removes cached files and temporary files when your device needs more space.
If storage on an iOS device differs from what you see in iTunes
Since iTunes categorizes cached files as Other, reported usage for Music or Videos might differ. To view usage on your iOS device, go to Settings > General > [Device] Storage.
If you want to delete the cached files from your iOS device
Your iOS device automatically deletes cached files and temporary files when it needs more space. You don't need to delete them yourself.
Here's a list of the types of content on your iOS device, and what each type includes:
- Audio: Songs, audio podcasts, audiobooks, voice memos, and ringtones.
- Video: Movies, music videos, and TV shows.
- Photos: Content in your Photo Library, Camera Roll, and Photo Stream.
- Apps: Installed apps. The content of the apps is listed under Documents & Data.
- Books: iBooks books, audio books, and PDF files.
- Documents & Data: Safari Offline Reading List, files stored within installed apps, and app content like contacts, calendars, messages, and emails (and their attachments).
- Other: Settings, Siri voices, system data, and cached files.
https://support.apple.com/en-us/HT201656