FixMyVideos vs untrunc

Let's start with the part most comparison pages bury: untrunc is free, open source, and genuinely good at the one problem it was built for. If you have a truncated MP4 or MOV and a healthy clip from the same camera, try untrunc before you pay anyone, including us. This page covers how it works, what the reference-clip requirement means in practice, and where it stops.

What untrunc is

untrunc is a command-line tool that restores truncated MP4, MOV, M4V and 3GP files. The original was written by Federico Ponchio. The version most people should use today is the anthwlock fork on GitHub, which is actively maintained (commits as recent as June 2026), runs roughly ten times faster, handles files over 2 GB, and copes well with GoPro and Sony XAVC recordings. The original ponchio repository has been mostly quiet since 2024.

Its README opens with a line we respect: "Provided you have a similar not broken video. And some luck." That is the whole model. untrunc reads the container structure of a working file from the same camera and uses it as a template to rebuild the missing index of your broken one. When the template matches, it works, and it works well.

At a glance

Getting untrunc running

Windows is the easy path. The fork's releases ship prebuilt binaries, and the zip includes a small GUI wrapper (untrunc-gui.exe), so you never touch the command line. Linux users build from source or install the snap package. On macOS there is no official binary; you install ffmpeg and yasm through Homebrew and compile it yourself. Third-party sites redistribute builds too; prefer the GitHub releases.

One quirk before you sink an evening into a build: untrunc is picky about ffmpeg versions. The maintainer recommends 3.3.9, and very new ffmpeg releases can break the build.

Where untrunc stops

Three walls come up in practice.

The reference clip is not optional. If the broken file is the only recording you have from that camera (a rented body, a friend's drone, a phone you sold last year), there is no template to copy, and the project's own README rates your chances without one as "slim."

The template has to actually match. Same camera is often not enough. Resolution, frame rate and recording mode all shape the container layout, so a 4K30 reference will not reliably rebuild a 1080p60 recording from the same body. People burn hours here without realising their settings differ.

It targets one class of damage. untrunc rebuilds a missing or broken index by copying a known-good structure. That is the truncation case, and it is a common one. If the damage sits elsewhere (corrupted codec parameter sets, an audio stream that needs reconstruction rather than re-indexing, a frame rate the container and the stream disagree about), a template copy can't reach it.

What FixMyVideos does differently

Instead of borrowing structure from a reference clip, our engine scans the broken file's own stream, finds the frame boundaries, reads the codec parameters from the frames themselves, and rebuilds the container metadata from what it observes. That is why no reference clip is needed for most cases. It runs in the browser, covers moov-atom loss, truncation and interrupted or power-loss recordings across MP4, MOV, MXF and insv, and reconstructs AAC and PCM audio alongside the video.

The trade is money for certainty. Upload and the 5-second preview of the recovered footage are free; you pay from $5 per file only if the preview proves the recovery worked. No working preview, no charge.

Honest recommendation

1. If you have a healthy clip from the same camera with identical settings, run untrunc first. It's free and built for exactly this.
2. On Windows, grab the fork's prebuilt zip and use the included GUI.
3. If there's no reference clip, or the output comes back silent or with the wrong duration, upload the file; the free preview tells you within about a minute whether our rebuild works.

What you do

1. Upload your corrupted file. In the browser, up to 50 GB.
2. About a minute later you get a free 5-second preview of the recovered video, picture and audio.
3. If it looks right, pay and download. If not, adjust settings or escalate to manual review. No charge until you have a working preview.

FAQ

Is untrunc free and safe? Yes. It's GPL-2.0 open source and runs entirely on your machine, so your footage never leaves your computer. For sensitive material that local-only property is a real advantage over any online service, ours included.

Which untrunc should I download? The anthwlock fork. It's the actively maintained one, much faster, handles files over 2 GB, and its Windows builds include the GUI. The original ponchio repository still exists but has seen little movement since 2024.

Can untrunc repair a file without a reference video? It needs one. The tool copies container structure from a healthy file, so without a similar working video the README itself calls the odds slim. FixMyVideos rebuilds from the broken file's own stream instead, so most cases need no reference at all.

untrunc ran but the output won't play properly. What now? Usually a template mismatch. Try a reference recorded with truly identical settings (resolution, frame rate, mode). If you can't produce one, or the output still comes out wrong, a stream-level rebuild is the next step, and the free preview shows quickly whether it works on your file.

Does FixMyVideos need a sample file like untrunc does? Not for most cases. The engine extracts codec parameters from the frames inside the damaged file. A reference clip helps only for a few unusual formats.

Is my footage safe if I upload it? Files go to an EU server, are auto-deleted after 48 hours, and are never shared or used to train anything. Privacy policy.

Related

• MP4 file truncated, repair guide
• GoPro Hero 12 truncated file
• FixMyVideos vs FFmpeg & Shutter Encoder
• FixMyVideos vs Stellar Repair for Video
• How our recovery engine works

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