Fix Broken Videos
with Untrunc

Yes, Untrunc is completely free to download and use. The software is released under the GNU General Public License version 2.0 (GPL-2.0), which means it is free for personal and commercial use with no license fees, subscription costs, or usage limits.

Both the command-line tool and the graphical user interface are included at no charge in the Windows ZIP download. There is no “Pro” or “Premium” tier, no trial period, and no feature that is locked behind a paywall. Untrunc is entirely community-maintained open-source software with no commercial interests behind it.

Compared to paid video repair tools like Stellar Repair for Video ($59), Wondershare Video Repair ($49.95), or Grau GmbH Video Repair Tool ($39), Untrunc delivers the same core moov atom reconstruction capability at zero cost. The only trade-off is that it lacks a polished interface and requires a healthy reference video from the same camera.

Pro tip: Download from the official anthwlock/untrunc GitHub Releases page or from our Download section above — both serve the same files directly from GitHub’s CDN. Avoid third-party mirror sites that bundle untrunc with adware installers.

See the Download section on this page for direct links to the Windows x64 and x32 builds.

Yes, Untrunc is safe to download and run on Windows 10 and Windows 11. The software is open-source (GPL-2.0) and the full source code is publicly available on GitHub, so anyone can audit it for malicious behavior. Multiple independent security researchers and antivirus vendors have scanned the Windows binaries and found no malware or adware.

You may see a Windows Defender SmartScreen warning the first time you run untrunc.exe or untrunc-gui.exe. This is a standard Windows behavior for downloaded executables that do not have a code signing certificate — most open-source tools trigger this warning, including many legitimate developer utilities. The warning does not mean the file is dangerous.

To proceed through the SmartScreen warning:

1. When the popup appears, click “More info” (the blue link at the bottom of the dialog).
2. A “Run anyway” button will appear at the bottom right — click it.
3. Untrunc will open normally and will not trigger the warning again for that executable.

Pro tip: If you want to verify the download yourself before running it, you can scan the ZIP file at VirusTotal.com by uploading it or pasting its SHA256 hash. Most results show 0-2 false positives, which is consistent with legitimate open-source software.

For complete peace of mind, download from our Download section, which links directly to the official GitHub release, not a third-party mirror.

Untrunc is extremely lightweight and runs on virtually any modern or older PC. The minimum requirement is Windows 7 SP1 (32-bit or 64-bit) with 256 MB of available RAM and 10 MB of disk space for the tool itself.

For the recommended setup, use Windows 10 or Windows 11 (64-bit) with at least 1 GB of RAM for processing large video files. The tool does not require a GPU, does not need .NET Framework, and does not require Visual C++ Redistributables beyond what comes with the ZIP. On 64-bit Windows 10 and 11, the tool runs as-is with no additional setup.

The key non-hardware requirement is a healthy reference video from the same camera. Without a matching reference file, Untrunc cannot reconstruct the moov atom regardless of how powerful the computer is.

• OS: Windows 7 SP1 or later (x86 or x64)
• CPU: Any 1 GHz or faster processor
• RAM: 256 MB minimum, 1 GB+ recommended for large files
• Disk: 10 MB for the tool, plus space for the repaired output file
• Internet: Not required after download — Untrunc works fully offline

Pro tip: The x64 build runs noticeably faster on large files (2 GB+) due to better memory handling. Always use the 64-bit version on 64-bit Windows unless you specifically need the 32-bit build for compatibility testing.

Full system requirements are listed in the System Requirements table above.

Untrunc repairs corrupted MP4 files by reconstructing the missing moov atom — the metadata block that tells media players how to read the video and audio tracks in the file. When a recording is interrupted before the camera finishes writing this atom, the file becomes unreadable despite containing all the raw video data.

The repair process works in three phases. First, Untrunc reads the moov atom from your healthy reference video, extracting the codec parameters (H.264 profile, resolution, frame rate, audio sample rate) and sample table structure. Second, it scans the damaged file from start to finish looking for raw video and audio frames that match the codec signature extracted from the reference. Third, it reassembles a new sample table that maps each found frame to its position in the file, then writes a new moov atom containing this table, producing the repaired output file.

The repair is lossless from a quality perspective. The raw video data in the broken file is never re-encoded or modified — only the index structure is rebuilt. Resolution, bitrate, frame rate, and audio fidelity are preserved exactly as originally recorded.

Pro tip: The repair works best when the reference video was recorded in exactly the same video mode as the broken file. A mismatch in frame rate (e.g., 30fps reference vs 60fps broken) or resolution can cause Untrunc to misidentify frame boundaries and produce a partially repaired or unplayable output.

See the Getting Started guide for step-by-step instructions on running a repair.

Untrunc requires a reference video because it uses that file’s moov atom as a template for rebuilding the missing metadata in the broken file. The moov atom contains codec-specific information — such as the exact H.264 parameter sets, track layout, and sample duration patterns — that is unique to each camera’s encoding configuration. Without a reference from the same camera, Untrunc has no way to know what codec format the broken file uses or how its frames are structured.

Think of the moov atom as a table of contents for the video file. The raw video data (the “mdat” atom) is still present in the broken file, but without the table of contents, media players cannot navigate it. The reference video provides an identical table of contents structure, which Untrunc adapts by scanning the broken file’s data to fill in the actual byte offsets and durations.

The reference video does not need to be from the same recording session — just the same camera in the same video mode. A 30-second clip filmed the same day works just as well as a multi-hour recording. The content (what was filmed) is irrelevant; only the technical encoding parameters matter.

Pro tip: Make a habit of keeping at least one short reference clip for each camera you own, stored on your computer where you can find it quickly. Many users keep a folder called “Reference Videos” with one clip per camera model and video mode (e.g., “GoPro-Hero12-4K60.MP4”).

If you truly have no reference video from the same camera, some users have reported partial success using a reference from the same camera model (different unit) in the same recording mode, though results vary significantly.

Yes, Untrunc supports macOS and Linux in addition to Windows. However, pre-built binaries are only provided for Windows — macOS and Linux users need to either build from source, use a package manager, or run a Docker container.

On macOS, the easiest installation method is Homebrew. With Homebrew installed, run brew install untrunc in Terminal. This downloads and compiles Untrunc with all required FFmpeg dependencies automatically. The process takes a few minutes on the first install but requires no manual dependency management afterward. The tool works on both Intel Macs and Apple Silicon (M1, M2, M3) Macs.

On Linux, you have three options:

1. Build from source: Install the FFmpeg development libraries (libavformat-dev, libavcodec-dev, libavutil-dev) and run make in the cloned repository directory.
2. Docker: Pull and run the rodolfoap/untrunc Docker image, which includes all dependencies pre-installed. This is the fastest option on Debian/Ubuntu.
3. Snap: On Ubuntu and other Snap-enabled distributions, install via the Snap store for a pre-packaged build.
4. Arch Linux (AUR): Install the untrunc-git AUR package using yay or paru.

Pro tip: The Docker method is the most reliable on Linux if you want to avoid dependency conflicts. Run: docker run --rm -v /your/video/folder:/data rodolfoap/untrunc reference.mp4 broken.mp4

See the Download section for platform-specific links to the GitHub repository.

Untrunc supports four video container formats: MP4 (.mp4), MOV (.mov), M4V (.m4v), and 3GP (.3gp). All four are based on the MPEG-4 container specification and share the same underlying atom structure, which is why the same moov atom reconstruction technique works across all of them.

Within these containers, Untrunc handles a wide range of codecs. For video, it works with H.264 (AVC), H.265 (HEVC), MPEG-4 Part 2, and Sony XAVC. For audio, it handles AAC, AC-3, and PCM tracks. The tool was specifically extended in the anthwlock fork to support GoPro’s custom MP4 extensions and Sony’s XAVC container variations used in Alpha and FX-series cameras.

Untrunc does not support AVI, MKV, WMV, FLV, or other non-MP4 container formats. For AVI repair, DivFix++ is an alternative. For MKV repair, mkvalidator or mkvmerge with error handling can recover some damaged files.

What Untrunc cannot fix:

• Files where the raw video data itself is corrupted (physical disk sector errors)
• Completely empty files (0 bytes)
• Files with an intact moov atom that plays incorrectly — that is a codec issue, not a container issue
• Non-MPEG-4 container formats (AVI, MKV, WMV, etc.)

Pro tip: If you are unsure whether your file is an MPEG-4 container, open it in MediaInfo (free tool) and check the Format field. If it says “MPEG-4” or “QuickTime,” Untrunc can likely repair it.

See the Features section for more on supported formats and codecs.

Yes, Untrunc is one of the most effective free tools for repairing corrupted GoPro MP4 files. GoPro cameras are among the most common sources of truncated video files because they record to microSD cards and write the moov atom only after a clean shutdown. When a GoPro powers off unexpectedly — due to a dead battery, a crash, or a card pulled mid-recording — the resulting MP4 lacks its moov atom and will not play.

The anthwlock fork of Untrunc includes specific handling for GoPro’s custom MP4 atom extensions (“GoPro metadata” or GMPD atoms). This means the repaired file retains the GoPro-specific metadata embedded in the recording, including GPS data from GPS-enabled models (Hero 5 and later), accelerometer and gyroscope data, and scene information used by GoPro’s editing software (Quik).

GoPro repair workflow:

1. Find a healthy GoPro file from the same camera in the same recording mode (same resolution, same frame rate, same EIS setting).
2. Run: untrunc.exe GoPro_reference.MP4 GoPro_broken.MP4
3. If the repair fails, try adding -s to skip unknown GoPro metadata atoms: untrunc.exe -s GoPro_reference.MP4 GoPro_broken.MP4
4. Verify the output file in VLC or GoPro Quik.

Pro tip: GoPro footage repaired with the -s flag may lose the embedded GPS/telemetry data, but the video and audio tracks will be intact. If you need the telemetry, try the repair without -s first, and only add the flag if the default repair fails.

Visit the Getting Started guide for the complete repair walkthrough.

Untrunc and Stellar Repair for Video are both effective video repair tools, but they target different users. Untrunc is better for technically comfortable users who have a reference video available and want a free, no-compromise solution. Stellar Repair for Video is better for users who want a polished GUI, do not have a reference video, and are willing to pay around $59 for a supported commercial product.

Here is a direct comparison:

• Price: Untrunc is free (GPL-2.0). Stellar Repair costs $59 per year for personal use.
• Reference video: Untrunc requires one. Stellar Repair has an “Advance Repair” mode that also needs a sample video, plus a “Quick Repair” mode that attempts repair without one (with lower success rates).
• Interface: Untrunc has a basic GUI and a CLI. Stellar Repair has a polished, beginner-friendly GUI with previews.
• Format support: Both support MP4, MOV, M4V. Stellar also supports MKV, AVI, FLV, MTS — formats that Untrunc cannot repair.
• Success rate: When a matching reference video is available, Untrunc generally achieves the same or better repair quality than Stellar’s Advance Repair mode for MP4/MOV files.
• Privacy: Untrunc runs offline and never uploads your video data. Stellar is also locally installed, but it is closed-source.

Pro tip: Try Untrunc first — it is free and the repair either works or it does not, with no financial risk. If you need to repair AVI, MKV, or FLV files, or if you have no reference video at all, Stellar’s Quick Repair mode is worth considering.

Download Untrunc from our Download section to try it at no cost before committing to a paid tool.

If Untrunc produces an unplayable output file or errors out during repair, the most common cause is a reference video that does not closely match the broken file’s encoding parameters. Work through these troubleshooting steps in order before concluding the file is unrecoverable.

1. Verify your reference video matches: Both files must come from the same camera model in the same recording mode (resolution, frame rate, video codec, audio codec). Open both files in MediaInfo and compare the Format Profile, Width, Height, Frame rate, and Codec fields. Any difference in these values is likely causing the failure.
2. Try a different reference clip: Sometimes a reference clip from the same day or a very similar recording session works better than an older clip. Try 2-3 different reference files.
3. Add the -s flag: Run untrunc.exe -s reference.mp4 broken.mp4. This tells Untrunc to skip atom types it does not recognize rather than aborting. It helps with files that contain GoPro or Sony-specific metadata atoms.
4. Check the broken file size: If the broken file is 0 bytes, the video data was never written and cannot be recovered by any tool. If it is very small (under 1 MB) for what should be a long recording, most of the data may be missing.
5. Enable maximum logging: Run with -log 4 and share the output on the GitHub Issues page. The log shows exactly where the repair fails and helps maintainers suggest a fix.
6. Try re-muxing the output: If the repaired file plays in VLC but not in other players, run ffmpeg -i broken_fixed.mp4 -c copy output.mp4 to re-mux it into a clean container.

Pro tip: The repair log will mention “unknown bytes” or “bad interleave” if the file structure is unusual. This is not necessarily a failure — Untrunc may still produce a usable output. Always check the resulting _fixed file even if the log shows warnings.

If none of these steps resolve the issue, open a GitHub issue with your camera model, video mode, file sizes, and the full -log 4 output for community assistance.

Untrunc does not include an auto-updater. To update to the latest Windows binary, visit the anthwlock/untrunc GitHub Releases page and download the most recent ZIP archive. Replace the old executables in your untrunc folder with the new ones from the downloaded ZIP.

The update process on Windows takes under a minute:

1. Go to the GitHub Releases page for anthwlock/untrunc.
2. Download the latest untrunc_x64.zip (or x32 for 32-bit systems).
3. Extract the ZIP to a temporary folder.
4. Copy the new untrunc.exe and untrunc-gui.exe (and any updated DLL files) into your existing untrunc installation folder, overwriting the old files.
5. Delete the temporary folder.

The latest release is dated 2020-03-24 from the anthwlock fork — the project reached a stable state and updates are infrequent. If you are already running the “latest” tag build, you have the current stable version. Some users track alternative forks such as fr0stb1rd/untrunc for more recent development activity.

Pro tip: Click the “Watch” button on the GitHub repository and select “Releases only” to receive an email notification whenever a new release is published. This way you do not need to check manually.

Alternatively, on macOS with Homebrew, simply run brew upgrade untrunc to update to the latest available version.

Yes, Untrunc handles files larger than 2 GB without any file size limit. The tool uses memory-efficient streaming to process files regardless of size, so it can repair multi-gigabyte 4K recordings, long security camera footage, and large RAW video files without running out of memory or hitting OS file size restrictions.

The 2 GB limit is a legacy restriction from older FAT32 file systems and 32-bit applications that used 32-bit file size integers. Untrunc’s 64-bit build (x64) uses 64-bit file addressing natively, so it can work with files up to the theoretical limit of your file system (4 TB+ on NTFS, exFAT, and ext4). Even the 32-bit (x86) build handles large files correctly because it uses proper 64-bit file I/O calls.

Processing time increases roughly linearly with file size. A 1 GB file typically repairs in under 30 seconds on a modern desktop. A 20 GB file may take 5-10 minutes. A 100 GB multi-hour security recording could take 30-60 minutes, though the actual time depends heavily on drive read speed (NVMe SSD vs mechanical HDD) and CPU clock speed.

Pro tip: If you are processing a very large file from a slow external drive, copy the broken file to a fast internal SSD before running Untrunc. This can cut processing time significantly since Untrunc does multiple sequential read passes over the broken file during sample scanning.

Make sure you have enough free disk space for the repaired output file, which will be similar in size to the original broken file. Check available space before starting a repair of a large file.

The moov atom is a metadata container within an MPEG-4 file (MP4, MOV, M4V, 3GP) that stores the structural index for all video and audio tracks in the file. It tells media players where each frame is located within the file, how long each frame lasts, what codec was used, what the resolution and frame rate are, and how the video and audio tracks are synchronized. Without it, the file’s raw media data is present but completely inaccessible to any player.

In a normally completed recording, cameras write the raw video frames continuously to the “mdat” (media data) atom throughout the recording, then write the moov atom in a single final operation at the very end of the recording. This is why interrupted recordings lose the moov atom: the camera ran out of power, the card was removed, or the recording application crashed before this final write operation completed.

Some cameras (and modern recording software) use a “moov-first” or “fragmented MP4” (fMP4) mode where the moov information is written progressively throughout the recording rather than just at the end. Files produced in fMP4 mode are naturally more resilient to interruption and typically do not need Untrunc. However, most consumer cameras use the traditional mode where moov is written last, making them vulnerable to truncation.

Pro tip: If you want to check whether a file has a moov atom, run ffprobe broken.mp4 (requires FFmpeg). If the output shows stream information, the moov atom is present and the file is likely playable. If ffprobe returns an error like “moov atom not found,” Untrunc is the right tool to try.

Learn more about how Untrunc reconstructs the moov atom in the Overview section above.

The official download for Untrunc Windows binaries is the anthwlock/untrunc repository on GitHub. The direct download links for the latest Windows builds are listed in the Download section on this page, which links directly to GitHub’s release CDN: github.com/anthwlock/untrunc/releases/download/latest/untrunc_x64.zip (64-bit) and untrunc_x32.zip (32-bit).

The original project by Federico Ponchio lives at github.com/ponchio/untrunc, but the original repository only provides Linux source code with no Windows binaries. For Windows users, the anthwlock fork is the standard recommendation across video repair communities, Reddit, and VideoHelp.com forums.

There are several third-party sites that host repackaged versions of Untrunc bundled with adware installers or additional software. Avoid these. You can identify safe downloads by checking that the file comes directly from github.com or codeload.github.com in your browser’s download dialog. If the download URL points to a third-party domain, do not use it.

The VideoHelp.com listing for “Untrunc GUI” also provides a clean download link directly from GitHub and is a trusted secondary source used by the video recovery community.

Pro tip: Bookmark the GitHub Releases page directly: github.com/anthwlock/untrunc/releases. This way you always get the most current official build rather than a potentially outdated cached copy from a mirror site.

Untrunc requires no installation and therefore has no uninstaller. Because the tool is a portable application distributed as a ZIP archive, removing it is simply a matter of deleting the folder where you extracted it. There are no registry entries, no system DLLs, no startup entries, and no user data stored outside the extracted folder.

Complete removal steps:

1. Close any open instances of untrunc.exe or untrunc-gui.exe.
2. Navigate to the folder where you extracted the Untrunc ZIP (e.g., C:\Tools\untrunc\).
3. Delete the entire folder. Send it to the Recycle Bin, or hold Shift+Delete to permanently delete it.
4. If you added the untrunc folder to your Windows PATH, open System Properties > Environment Variables > Path, find and remove the entry.
5. That is all — there is nothing else to clean up.

You can verify the removal by searching your Start menu for “untrunc” — nothing should appear. The Windows Registry contains no untrunc entries because the tool never writes to it.

Pro tip: Before deleting, consider whether you want to keep your reference video files. Those are separate from the Untrunc tool and exist wherever you stored them. The tool itself leaves no trace of what files it processed.

If you want to reinstall in the future, simply download a fresh ZIP from our Download section and extract it to a new folder.

Yes, Untrunc works entirely offline. Once downloaded, the tool requires no internet connection to function. The repair process reads two local files (the reference video and the broken video) and writes one local output file. No data is uploaded, no license server is contacted, and no telemetry is sent anywhere.

This matters for users repairing sensitive footage — security camera recordings, legal evidence video, private footage, or confidential professional productions — where uploading files to cloud-based repair services would be inappropriate. Untrunc processes everything locally on your own hardware, so your video content never leaves your machine.

The only online activity associated with Untrunc is the initial download from GitHub and any voluntary community interaction (submitting issues, checking for updates). The executables themselves contain no network code beyond what the operating system provides.

This also makes Untrunc suitable for air-gapped environments such as law enforcement forensics workstations, secure government systems, and corporate networks with strict outbound traffic restrictions. You can copy the extracted ZIP folder to a USB drive and run it on any Windows computer, connected or not.

Pro tip: If you need to regularly repair footage on an offline workstation, keep a copy of the Untrunc ZIP on a USB drive along with your reference video collection. This gives you a complete portable repair kit that works anywhere without internet access.

Download Untrunc once from our Download section and it works indefinitely with no required connection.

Yes, Untrunc can repair DJI drone MP4 files that were truncated due to a mid-flight crash, battery depletion, or storage card error. DJI cameras (on Mavic, Mini, Phantom, Inspire, and Action series) record in standard MP4 and MOV containers with H.264 or H.265 video, making them compatible with Untrunc’s moov atom reconstruction technique.

DJI drone repairs are a common use case in the Untrunc community. Forum posts and GitHub issues from DJI users report successful recovery of footage from crashed Mavic 3, Mini 3 Pro, and FPV drone recordings where the drone lost power mid-flight and the SD card was recovered from the wreckage. The key is having a healthy reference clip from the same drone in the same video mode.

DJI-specific repair tips:

1. Match the video mode exactly: resolution (4K/2.7K/1080p), frame rate (24/25/30/60fps), and codec (H.264 or H.265). DJI’s H.265 and H.264 modes produce different moov atom structures.
2. DJI files contain proprietary metadata atoms (DBGI, DBGX). If the default repair fails, try adding -s to skip these atoms.
3. Some DJI models split long recordings into 4 GB segments. Repair each segment individually with the same reference file.
4. D-Log and Normal color profiles can affect codec initialization in subtle ways. Use a reference filmed in the same color profile as the broken file when possible.

Pro tip: After a successful DJI repair, run the output through DJI’s own editing tools or ffprobe to verify the embedded telemetry (GPS, altitude, speed) is intact. The telemetry atoms are often preserved even when -s is used, but it is worth checking if that data matters to you.

See the Getting Started guide for the complete repair workflow.

Using Untrunc on the command line is straightforward once you understand the two-file syntax. The entire repair operation is a single command: you provide the path to the healthy reference video first, then the path to the broken video. Untrunc writes the repaired file to the same folder as the broken video automatically.

Step-by-step CLI guide for Windows beginners:

1. Press Windows key + R, type cmd, and press Enter to open Command Prompt.
2. Navigate to your untrunc folder: cd C:\Tools\untrunc (adjust the path to where you extracted the ZIP).
3. Type the repair command. Replace the paths with your actual files:
   untrunc.exe "C:\Videos\reference.mp4" "C:\Videos\broken.mp4"
4. Press Enter. Watch the output. Progress lines appear as Untrunc scans the broken file.
5. When done, look for the line: Output: broken_fixed.mp4
6. Find the _fixed file in the same folder as your broken video and verify it plays.

If your file paths contain spaces (which is common), always wrap them in double quotes, as shown above. Without quotes, Command Prompt treats spaces as argument separators and misinterprets the paths.

Useful optional flags to know:

• -s — Skip unknown metadata atoms (try this if the default repair fails)
• --stretch — Fix audio-video sync in the repaired file
• -log 2 — Show more detail in the progress output (0=quiet, 4=maximum)

Pro tip: You can drag and drop file paths from Windows Explorer into the Command Prompt window to avoid typing long paths. Drag the reference file first, add a space, then drag the broken file. The paths appear with correct quotes automatically in newer versions of Windows.

Prefer a graphical interface? See the Getting Started guide for GUI instructions.