How to Convert a Video to MP4 on iPhone

The fastest way to convert a video to MP4 on iPhone is to re-export the clip from an editor, that resolves both the container and the codec at once. Here's what's actually causing the playback problem, and how to stop it happening to future clips. The short version: the file extension is rarely the real issue, and changing it alone doesn't fix anything.

Convert a video to MP4 on iPhone

Bring the clip into an editor and export it as an .mp4. That single export handles both the file container and, if needed, the codec encoded inside it.

Container vs codec: what actually breaks playback

.mov and .mp4 are containers. Think of them as the box a video ships in, describing how the audio, video and metadata are packaged together. HEVC (H.265) and H.264 are codecs. What's actually inside the box, the method used to compress the picture itself. A file that refuses to play somewhere is almost always a codec problem, not a container one: renaming a .mov to .mp4 doesn't change a single byte of the video data inside it, so it fixes nothing if the codec was the real issue.

HEIF/HEVC has been supported across Apple's ecosystem since 2017 (iOS 11), so playback trouble usually shows up on older systems or software outside that range. An older Windows PC without an HEVC codec pack installed, or a web tool that only decodes H.264, being the two most common cases.

Settings > Camera > Formats > Most Compatible switches new recordings to H.264, which plays more widely — but it only applies going forward. It won't touch a clip you've already recorded, which is why an existing file with playback problems still needs a re-export rather than a settings change.

HEVC exists because it stores the same picture quality in roughly half the data of H.264, which is why Apple made it the default in 2017. Smaller files mean less storage used per recording and less data moved when a clip is shared. The trade-off is exactly the compatibility problem this page is about: software written before HEVC existed, or software that never added support for it, can't decode it at all.

One export, one predictable file

Montaj exports in HEVC (.mp4). A single, normalized output rather than a mix of formats depending on how the original was recorded, whether that original arrived as a screen recording, a download, or a clip shot on an older device with a different codec. Once you've converted a video to MP4 on iPhone this way, you're exporting one predictable file type every time, instead of inheriting whatever format the source happened to be in.