The best there is for iOS

One of the first things I do after I install Windows is download VLC. Since 2018, Infuse has been the VLC for my iPhone and iPad. It plays everything perfectly fine with zero hiccups. My only gripe that I had with Infuse for a while was that it did not have variable playback speeds (Play at 1.5x, 2x, etc.), but a few years ago they finally added that. I spent $100 and got the “lifetime upgrade” pass so I download each new version as they are released. I am a lifelong fan and will likely never change since it essentially has everything I need.