How to Convert MOV to MP4 on a Mac (Without Re-encoding)

Your Mac and your iPhone record .mov. The site, the form or the Windows PC you send it to wants .mp4. In most cases the video inside is already the right kind — it is the wrapper that is wrong, and swapping a wrapper takes seconds and costs no quality.

Three routes below, all built into macOS, all measured on the same file: a 29-second screen recording, 3,215,044 bytes, H.264 video with AAC audio.

What is actually different about a .mov

A file format has two layers: the container (the box) and the codec (what is in the box). .mov is Apple’s QuickTime container; .mp4 is the MPEG-4 one. Both normally carry H.264 or HEVC video and AAC audio — the same codecs.

You can see which box a file is in by reading its first bytes. The recording we measured identifies itself as qt; a real MP4 says mp42. That four-letter stamp is what a strict uploader looks at, and it is the entire problem.

Route 1: rename the file (fast, and only half true)

Select the file, press Return, change .mov to .mp4, confirm when Finder asks.

What we measured: the renamed file was byte-for-byte identical to the original — same 3,215,044 bytes — and still stamped qt inside. macOS played it without complaint.

So it works, right up until it does not. Anything that trusts the extension opens it; anything that reads the container rejects it, and the error you get (“unsupported format” on a file that plays fine at home) is baffling precisely because the file looks converted and is not. Fine for sending to a friend. Not fine for an upload form that has already refused you once.

Route 2: the converter already on your Mac (2 seconds, no quality lost)

macOS includes a command-line converter called avconvert. Nothing to download, nothing to trust. Open Terminal and run:

avconvert --preset PresetPassthrough --source in.mov --output out.mp4

Drag the file into the Terminal window instead of typing the path, and it fills itself in.

What we measured: 3,215,044 bytes in, 3,167,536 bytes out, in 2.0 seconds (repeated: 2.03 s and 2.05 s). The output is stamped mp42 — a real MP4 — and the video stream is untouched H.264. The file came out very slightly smaller because the conversion strips source metadata rather than because anything was compressed.

PresetPassthrough is the important word. It copies the existing streams into the new container instead of re-encoding them, which is why it takes two seconds rather than a minute and why the picture is identical rather than a generation worse.

Route 3: export from an app (re-encodes — and can make the file bigger)

QuickTime Player’s File → Export As and Finder’s Quick Actions → Encode Selected Video Files both hand the video to macOS’s export presets. Those presets re-encode: they decode your video and encode it again at their own target.

What we measured, using the same preset a 720p export uses: 3,215,044 bytes in, 5,287,139 bytes out — 64% larger — and 5.1 seconds instead of 2.0.

That is not a bug. An export preset encodes to the bitrate it was designed for, whether or not the source was already below it. It is the single most common surprise in video conversion, and it is why “export at 1080p” is the wrong tool when what you wanted was the same video in a different box.

If you genuinely need a smaller file — a Discord limit, an email attachment that bounces — that is a different job from changing the container, and it needs a route that reads the source bitrate first and aims below it.

Which one to use

You want	Use
It to play on someone else’s machine, right now	Rename it (Route 1)
A real MP4 an upload form will accept	avconvert passthrough (Route 2)
A different resolution or a smaller file	An export route, knowing it re-encodes (Route 3)

What none of these do

They will not open formats macOS cannot read. MKV, WebM and WMV are not supported by the system’s video stack at all, so no built-in route converts them — that genuinely needs third-party software.

They will not write MP3. Extracting audio with the built-in tools gives you M4A. It plays everywhere a modern device is involved, but if something specifically demands MP3, macOS will not produce it on its own.

Route 3’s numbers are ours, not a rule. A 3.2 MB screen recording is already efficiently encoded, which is why re-encoding inflated it. A large, badly compressed camera file may well shrink under the same preset. The lesson is not “export always inflates” — it is “check the result, because a preset does not know what your source was”.

Does ComfortFiles do this?

Not today — and rather than imply otherwise: ComfortFiles is a file manager, and video conversion is not among the file jobs it currently handles. What it does handle is the surrounding work — browsing and previewing files, batch renaming the clips once they are converted, and PDF and image jobs done on your own Mac with nothing uploaded. If video tools belong there too, that decision will be made from what people actually ask for.

Frequently asked questions

Can I just rename a .mov file to .mp4?

It will usually play, and it is not really converted. Renaming changes the four letters after the dot and nothing inside the file: a QuickTime recording still identifies itself as QuickTime, which is why some upload forms and players reject it while others open it happily. Measured on a screen recording: the renamed file was byte-for-byte the original, still stamped qt internally rather than mp42.

How do I convert MOV to MP4 on a Mac for free, without installing anything?

macOS ships a converter you already have. In Terminal: avconvert --preset PresetPassthrough --source in.mov --output out.mp4. Passthrough copies the existing video and audio into an MP4 container instead of re-encoding them, so there is no quality loss and it takes seconds — 2.0 seconds for a 3.2 MB, 29-second recording in our measurement.

Does converting MOV to MP4 lose quality?

Only if something re-encodes the picture. A container swap (remux) copies the same video stream into a different wrapper and loses nothing. Every "export at 1080p" route re-encodes, which both loses a generation of quality and takes longer.

Why did my video get bigger after converting it?

Because an export preset is not compression. Asked to export the same 3.2 MB recording at 720p, macOS returned 5.3 MB — 64% larger — because a preset encodes to its own target bitrate whether or not that is higher than the source. If the goal is a smaller file, choose a route that reads the original bitrate first.

Why does my iPhone record .mov instead of .mp4?

QuickTime is Apple's own container format and the Camera app writes it by default. The video inside is normally H.264 or HEVC — the same codecs an .mp4 carries — which is exactly why a container swap works and a full re-encode is unnecessary.