VLC media player

From the app store
VLC for Mobile is a port of the free VLC media player to iPad, iPhone and iPod touch.
It can play all your movies, shows and music in most formats directly without conversion.
It allows file synchronization with Dropbox, GDrive, OneDrive, Box, iCloud Drive, iTunes, direct downloads and through WiFi sharing as well as streaming from SMB, FTP, UPnP/DLNA media servers and the web.
VLC offers support for advanced subtitles including full SSA compatibility, multi-track audio, and playback speed control.

VLC for Mobile is completely free and open source.