MOV vs MP4: what's the difference?

MOV and MP4 are both containers: file formats that hold video and audio. What decides quality and file size is the codec inside, and a codec like H.264 fits in either one. So a MOV with H.264 video can become an MP4 without re-encoding, by moving the same data into a new box (a remux). You only need to re-encode when the file holds a codec the other person’s device might not play.

Containers and codecs are different things

MDN describes a media container as a file format that holds one or more media streams, such as audio or video, along with metadata, so they can be stored and played back together. A codec is the method used to compress and decompress those streams.

Layer	What it does	Examples
Container	Holds video, audio and metadata in one file	MOV, MP4, WebM, MKV
Video codec	Compresses the picture; drives quality and size	H.264 (AVC), HEVC (H.265), VP9
Audio codec	Compresses the sound	AAC, MP3, Opus

Think of the container as a box and the codec as the way its contents are packed. The .mov and .mp4 extensions are just names on the box, so the extension alone doesn’t tell you which codec is inside.

What MOV and MP4 share, and where they differ

MOV is the QuickTime file format that Apple developed. According to MDN, the MP4 file format is derived from the ISO base media file format, which was itself derived directly from the QuickTime file format. The two are close relatives.

Item	MOV (QuickTime)	MP4 (MPEG-4)
Extension	.mov	.mp4
H.264 video	Supported	Supported
HEVC (H.265) video	Supported	Supported
AAC audio	Supported	Supported
Where it’s used	Mainly Apple devices	Broadly supported on the web and many devices

The real difference is reach. MDN calls MP4 a popular container that supports several of the most-used codecs and is broadly supported. QuickTime, on the other hand, is mainly available on Apple devices, so MDN notes it’s no longer widely used on the internet. That’s why MP4 is the safe choice when you don’t know what device or app the other person uses.

iPhone videos and HEVC

According to Apple Support, iPhone 7 and later models running iOS 11 or later can record video in HEVC (H.265). HEVC compresses better than H.264, so it uses less storage. You choose the capture format in Settings → Camera → Formats. Most Compatible saves new photos and videos as JPEG and H.264. High Efficiency uses HEIF and HEVC.

The catch is playback. MDN shows that browser support for HEVC depends on the operating system and hardware. So when a .mov file won’t open on some device, the cause may be the HEVC codec inside, not the extension. Apple says that when you share through AirDrop, Messages or email, media might automatically be shared in a more compatible format such as H.264 if the receiving device doesn’t support the newer one. That’s a “might”, though. If you don’t know the recipient’s setup, converting to an H.264 MP4 yourself is the surer path.

Remux vs re-encode

There are two ways to turn a MOV into an MP4:

• Remux: the codec data stays as is and only the box changes. The video isn’t compressed again, so quality doesn’t change and the size stays about the same.
• Re-encode: the video is decoded and compressed again with another codec, such as H.264. This fixes codecs the recipient can’t play, but it goes through lossy compression one more time, so quality may differ slightly from the original.

Convert to MP4 re-encodes only the parts of each file that need it:

Original	What happens	Message on the result
H.264 video + AAC or MP3 audio	Remux	“Changed the format without re-encoding”
H.264 video + other audio	Video kept, only the audio converted to AAC	“Video kept as is; only the audio was converted to AAC”
Other video (HEVC, VP9 and so on)	Re-encoded to H.264 at the same resolution and fps	“Re-encoded to H.264”

If you turn off “Maximize compatibility (convert to H.264)”, HEVC video also moves into the MP4 without re-encoding. Turn it off only when you know the recipient can play HEVC.

Here’s what happened with our test files (measured in desktop Chrome; results vary by device and browser):

Original	Result
MOV (H.264 + AAC, 720p, 10 s), 1.1 MB	Remuxed, MP4 1.1 MB
WebM (VP9 + Opus, 640×360, 10 s), 829 KB	Re-encoded to H.264 + AAC, MP4 742 KB
AVI (MJPEG + PCM, 640×360, 5 s), 2.2 MB	H.264 + AAC MP4, 527 KB

How to do it with ZEKILO Studio

Convert to MP4 works inside this browser, and your file never leaves your device.

1. Drag and drop one video or pick it with [Choose files]. The length, resolution and codecs appear, so you can see which codec is inside.
2. Check that “Maximize compatibility (convert to H.264)” is on (the default), then press [Start].
3. Play the result to check it, then save the MP4 with [Download]. Only the extension changes, as in clip.mov → clip.mp4.

You can add one video at a time. We recommend up to 1 GB on desktop and 100 MB on mobile. AVI, WMV and FLV files are processed with a fallback engine (FFmpeg), so for those we recommend up to 300 MB on desktop and 100 MB on mobile, and files over 700 MB are not processed. A remux keeps the size about the same, so if you also need a smaller file, use Compress Video. Its result is always an H.264 + AAC MP4. For step-by-step tips, see how to shrink a video for email and messaging apps.

Summary

• MOV and MP4 are containers (boxes). The codec inside, such as H.264 or HEVC, decides quality and size.
• Both can hold H.264 and HEVC, but MP4 is more broadly supported.
• A MOV with H.264 + AAC becomes an MP4 through a remux, with no change in quality. HEVC, VP9 and similar codecs open on more devices once re-encoded to H.264.
• If a file won’t open, check the codec inside before you blame the extension.