Understanding the "264 MP4" relationship requires distinguishing between a and a container :
This is the "box" that holds the H.264 video stream, along with audio (typically AAC), subtitles, and metadata. Why They Are Used Together 264 mp4
Does anyone have strong opinions about using h264 for proxy media? along with audio (typically AAC)
This is the "brain" that compresses and decompressess the raw video data to make it small enough for storage and streaming. 264 mp4