mp4 H264 video won't play in iPhone safari
MP4 is a container format, while H. 264 is a video compression codec. So to play H. 264 in Safari, you will need a video container like MP4 to host the encoded video.
Settings based on the MPEG-4 format offer a choice of two encoders: H.264 and HEVC (High-Efficiency Video Coding, also known as H.265). When you add an MPEG-4-based setting to a job, Compressor chooses the H.264 format as the default codec. You can change the codec to HEVC in the Video inspector if your computer is running macOS 10.13 or later. HEVC is a recently established compression standard that supports larger frame sizes (including 8K) and HDR10 metadata for high-dynamic-range video. HEVC playback requires a recent-generation Apple device running macOS 10.13 or later, iOS 11 or later, iPadOS 13 or later, or tvOS 11 or later.