What MOV to MP4 actually writes
A MOV from an iPhone plays on a Mac and then fails, or plays silently, on a Windows PC or in a browser.
The MOV is re-encoded to MP4 with MPEG-4 video and AAC audio. The first run downloads the converter library. Stay on the tab.
Quality and the MOV file you should keep
This is a new encode, not a lossless remux. If you only needed a rename and the video was already H.264, a desktop remux keeps more quality than this page does.
A related step, if you still need one, is MP4 to MOV.
When MOV to MP4 is the right page
MOV to MP4 sits on this site because MOV and MP4 are not interchangeable, even when they look similar in a file list. A MOV from an iPhone plays on a Mac and then fails, or plays silently, on a Windows PC or in a browser. Windows PCs and some browsers play MOV with no sound or refuse it, which is why people make an MP4. Phones, browsers, Instagram, YouTube, and WhatsApp all expect MP4.
The MOV is re-encoded to MP4 with MPEG-4 video and AAC audio. The first run downloads the converter library. Stay on the tab.
What you give up by leaving MOV
MOV is the QuickTime container Apple devices record. It often plays on a Mac. A browser conversion re-encodes it. It does not copy every audio track losslessly.
Keep the camera MOV until the MP4 plays with sound on the device that failed.
What you gain, and do not gain, with MP4
The download has to be MP4, because that is the format the next step named. Phones, browsers, Instagram, YouTube, and WhatsApp all expect MP4. If the other person can open only one video format, MP4 is that format.
A new encode cannot look cleaner than the MP4 you started with. A remux on a desktop is the lossless path when the streams are already compatible.
A test that matches the real file
Start from the question the other software asked. If it asked for MP4, MOV to MP4 is the matching page. If it asked for something else, switch tools instead of hoping a similar extension will pass. A MOV from an iPhone plays on a Mac and then fails, or plays silently, on a Windows PC or in a browser. The MOV is re-encoded to MP4 with MPEG-4 video and AAC audio. The first run downloads the converter library. Stay on the tab. The limit is the part people skip, and it is the part that decides whether the download is usable. This is a new encode, not a lossless remux. If you only needed a rename and the video was already H.264, a desktop remux keeps more quality than this page does. The file stays on your device. The first run downloads a converter, so keep this tab open. A phone runs out of memory on long files. A computer is the safer place for a big clip. Check three things in the download: it opens, the MOV material you cared about is still there, and the file size or the layout is what the form described. A new extension alone is not those three things. If a portal, a teacher, or a client rejects the file, send them the original MOV as well when you are allowed to. MOV to MP4 is a convenience copy. It is not a new master. Video files hide the real problem inside the container. MOV to MP4 re-encodes on your device. It does not silently copy every audio language and every subtitle the way a desktop remux can. If you needed those extra tracks, this download is the wrong result even when the picture plays. Convert a one-minute piece before a full movie, and stay on the tab while the converter downloads the first time.
Here is the decision for MOV to MP4. You start with MOV and you stop when a real program accepts MP4. On Apple software it is a normal camera file. Soft subtitles such as ASS or PGS, and extra audio languages, are awkward or dropped when a tool re-encodes. If those two sentences describe a tradeoff you do not want, do not convert. Renaming the extension by hand will not do this job. Running the tool twice on its own output will not do it either.
This is a new encode, not a lossless remux. If you only needed a rename and the video was already H.264, a desktop remux keeps more quality than this page does.
A related step, if you still need one, is MP4 to MOV.
Other jobs start from the homepage, where each tool is named for the conversion it actually does.