CapCut says 'file not supported': what's actually wrong

CapCut is reading what is actually inside the file, not the three letters on the end of its name. Its own help centre puts it bluntly: even with a common extension, its actual format may not be supported by CapCut. The import target that reliably works is H.264 video with AAC audio in an MP4 container.

The files that usually fail are HEVC clips from a recent iPhone or Android, a MOV straight off a camera, an MKV that somebody renamed to .mp4 by hand, or an AV1 download. Convert to H.264 MP4 and the import goes through.

Why a file called .mp4 is not necessarily an MP4

A video file has two layers, and people conflate them constantly. The container is the box: MP4, MOV, MKV, WebM, AVI. It holds the streams, the timestamps and the metadata. The codec is what the picture is compressed with: H.264, H.265 (also called HEVC), VP9, AV1, MPEG-4 Part 2, ProRes.

The extension only ever describes the box. An MP4 can legally contain H.264, HEVC, AV1 or MPEG-4 Part 2, and CapCut treats those four very differently. That is why two files that both say .mp4, both play fine in your phone's gallery, and both look identical in Files, can get opposite answers from the importer.

The second half of the trap is renaming. Changing holiday.mkv to holiday.mp4 does not touch a single byte — it puts a misleading label on a box that is still Matroska. CapCut reads the header, sees Matroska, and refuses. Players are forgiving about this; editors are not, because they have to seek around inside the file rather than just play it through.

The files that usually fail

HEVC from a modern phone

iPhones set to High Efficiency record HEVC in a MOV wrapper. Recent Android phones do the same into an MP4. HEVC is the single most common cause of an import that dies on a file the gallery plays perfectly, because gallery playback uses the hardware decoder while an editor needs to decode, seek and re-encode. To stop it at source on iPhone, set Settings > Camera > Formats to Most Compatible; new recordings will be H.264. That does nothing for footage you already shot, which is what the HEVC to H.264 converter is for. The same codec is behind a whole family of complaints, including HEVC files refusing to play on Windows 11.

MKV, renamed or not

MKV is a download and archive format. CapCut on mobile does not import it, and renaming it does not help. Because Matroska usually holds ordinary H.264 or HEVC video, moving it into an MP4 box is often a stream copy rather than a re-encode: seconds, and bit-for-bit identical picture. That is exactly what the MKV to MP4 converter does. If the MKV turns out to hold HEVC, set the video codec to H.264 in the advanced options so it re-encodes instead of copying, or CapCut will reject the MP4 for the same reason it rejected the MKV. Desktop editors hit the same wall — see why Premiere Pro will not import MKV.

AV1 and VP9 downloads

Video pulled from the web is increasingly AV1 or VP9, in a WebM or an MP4. Neither is a safe editing codec on a phone, and both need a real re-encode to H.264 — there is no shortcut, because the picture has to be decompressed and compressed again.

MOV from a camera or a screen recorder

A MOV holding H.264 and AAC is the easy case: MP4 and MOV are both ISO base-media containers, so swapping the box is a copy. A MOV holding ProRes, a screen-recording codec or HEVC is not. Our MOV to MP4 converter tells you which of the two you have before you press anything.

HDR and 10-bit footage

Dolby Vision and HDR10 recordings are HEVC with extra colour metadata attached. Some devices import them, some refuse, and some import them with the colours visibly wrong.

Check what is inside before you convert anything

Guessing wastes a re-encode. Drop the file onto our converter page and it reads the header locally: container, video codec and profile, resolution, frame rate, audio codec, and how many subtitle and extra audio tracks are riding along. Nothing is uploaded to check this. There is a longer walkthrough in the guide on checking a video's codec online.

Read the codec line first. If it says hevc, av1, vp9, prores or wmv3, you need a re-encode. If it says h264 and the container is anything but MP4, you only need the box changed, which is fast and lossless.

What to convert to

Two things worth knowing. A stream copy — codec already fine, only the container changes — is near-instant however long the clip is, and the picture is untouched. A re-encode is not lossless at any quality setting, and in a browser it is slow: the build is single-threaded, so budget around real time for 720p and worse for 1080p. Files above 2 GB are refused, and above roughly 300 MB the page warns you, because converting needs about three times the file size in free memory.

Subtitle tracks and any audio track after the first are dropped in conversion. That rarely matters for a CapCut import, but it is worth knowing if you were counting on a second language track.

Doing this on a phone

Most people hitting this error are mid-edit on a phone, and a phone browser is the worst place to run a converter: mobile Safari and Chrome reclaim memory from background tabs aggressively, and a long 4K clip will run out of room. For a short clip the browser tool is fine. For anything long, do it on the device instead.

The Video Converter app for iPhone and the Android version convert between MP4, MOV, AVI, MKV and 3GP straight from the camera roll, using the phone's hardware encoder — which is why they are far quicker than any browser on long or 4K footage, and why they have no file-size ceiling. They always re-encode rather than copying, and they do not show you the codec, so if you need to be certain the output is H.264 the browser tool is the one that lets you set it explicitly. On iPhone the first conversion is free and further ones need the paid upgrade; the Android app is free and unlimited. If you are converting camera-roll footage regularly, the guide on converting MOV to MP4 on iPhone covers the workflow in more detail.

What converting cannot fix

• DRM-protected files. Anything downloaded for offline viewing from a streaming service is encrypted. No converter can open it, ours included, and the error you get from CapCut will look identical to a codec problem.
• Cloud placeholders. If the clip lives in iCloud Photos or Google Photos and has not been downloaded to the device, there is no file to import yet. Open it in the gallery, wait for it to finish downloading, then try again.
• Permissions and storage location. CapCut needs photo or media access, and on Android files sitting on an SD card or in an app-private folder are sometimes unreachable. Move a copy to internal storage.
• Account and sign-in errors. A message about your account, a region, or a template is not a format problem and converting will not touch it.
• A truncated file. If a download or transfer was interrupted, the header may be incomplete. Our converter will usually fail to read it at all, which is itself a useful signal.

It imported, but something is wrong

If the clip lands on the timeline with no sound, the original almost certainly carried AC-3, DTS or another codec that got dropped; re-converting with the audio set to re-encode to AAC is the fix, and the guide on video that plays with no sound works through the causes.

If the audio drifts further out of sync the longer the clip runs, you are looking at variable frame rate footage — normal for screen recordings and phone captures, and poison for editors that assume a fixed rate. Converting with the frame rate pinned to 30 solves it; the guide on converting variable frame rate to constant explains why the drift accumulates.

If playback stutters but the file is otherwise fine, the clip is too heavy for the device: convert again at 1080p rather than 4K. And if the finished export is too big to send, the same settings solve that — see converting video for WhatsApp.