Convert a MOV file to MP4 without re-encoding it in the common case. MOV and MP4 come from the same file format family, and the codecs an iPhone or a camera records fit both.
What an iPhone MOV contains
Recent iPhones record HEVC video and AAC audio in a MOV container; older models, and the Most Compatible camera setting, record H.264. Both codecs are copied into the MP4 as they are, so the conversion takes about as long as reading the file and the picture is identical.
HEVC compatibility
An HEVC file is roughly half the size of an H.264 file of similar quality, but not everything plays it. Upload forms and older editors are the usual problem. The Re-encode video switch produces H.264 instead, at the source size and a high quality setting.
ProRes and other camera formats
ProRes MOV files from cameras and editing software are re-encoded to H.264. The result is a fraction of the size and plays anywhere, but ProRes exists to survive heavy grading, so keep the original for editing work.
Metadata
Rotation is kept. Other metadata tags, such as the recording location and camera model, are not copied into the MP4.