Untrunc

Untrunc is a free, open-source utility for repairing certain damaged or truncated MPEG-4 videos. It suits people with a healthy clip from the same camera and recording settings, especially those who want to keep footage on their own device. Its focused repair method is useful when a file’s structure is the problem, but it cannot fix damaged raw video data.

Overview

Untrunc reconstructs missing or damaged index metadata in MP4, MOV, M4V, and 3GP files. It rebuilds the file structure without re-encoding or modifying the underlying media, so it is aimed at files whose raw video data remains intact. It cannot recover empty files or repair corrupted raw video, and it does not support containers such as AVI or MKV.

A healthy reference video is essential. It should come from the same camera and use the same recording settings as the damaged file, which makes Untrunc a poor fit when no suitable clip is available. Repairs run offline on local files, with no uploads or telemetry—a meaningful privacy advantage for sensitive footage.

Key features

• Reference-based repair: The reference clip provides the basis for reconstructing file structure. Without a matching sample, the core repair workflow is unavailable.
• No re-encoding: Untrunc repairs structure without changing raw media data. That keeps the tool focused on metadata problems rather than attempting to restore damaged picture or sound data.
• Large-file handling: There is no file-size limit, and streaming mode can process files larger than available RAM. This is useful for long recordings without requiring a machine to hold the entire file in memory.
• Audio adjustment: Optional stretch mode can adjust audio duration to match the recovered video track, which may help when the recovered tracks differ in duration.
• Camera support: The project describes support for GoPro footage and Sony XAVC. The anthwlock fork adds compatibility and performance improvements.
• Local, open-source operation: The software runs offline, is released under GPL-2.0, and is free for personal and commercial use. Technical support is directed to the anthwlock GitHub Issues page; the informational website does not provide software support.

Pricing

Free — free. The software is free to download and use, with no license fees or subscriptions, no usage or file-size limits, and GPL-2.0 licensing. This is the only plan described, so there is no paid tier to add convenience or support. The trade-off is that users must supply a healthy reference video from the same camera and recording settings, and technical help is directed to the project’s issue tracker.

Platforms

Untrunc supports Windows, macOS, and Linux, with local repair on each. The Windows download includes both a graphical interface and a command-line tool; other platforms use a command-line workflow. That gives Windows users a GUI option, while users on macOS and Linux should be comfortable working from the command line.

Who it's for

Untrunc is aimed at action-camera users, drone pilots, dashcam owners, screen recorders, security-camera operators, and videographers whose MP4, MOV, M4V, or 3GP file has a structural problem and who can provide an appropriate reference recording. It is not the right choice for AVI or MKV files, empty files, footage with corrupted raw media, or situations where no matching reference exists.

Pros and cons

• Pros: Free for personal and commercial use, with no usage or file-size limits, so large repairs do not trigger a quota or subscription.
• Pros: Offline local processing with no uploads or telemetry suits users who want footage to stay on their device.
• Pros: Repair does not re-encode or modify raw media, preserving the original data while addressing file-structure problems.
• Cons: A healthy clip from the same camera and recording settings is required, which can rule it out when users lack a suitable reference.
• Cons: Support is narrow: it handles four listed MPEG-4 container formats and cannot repair empty files or corrupted raw video data.
• Cons: The command-line workflow on macOS and Linux may be less approachable than the Windows graphical interface.

Alternatives

For a different video repair workflow, IntactFile has a free plan with three repairs per day, videos up to 50 MB, and no-account use; it also supports documents, archives, and photos under their stated size caps. Choose it when those daily limits and broader file categories suit the job better than Untrunc’s reference-based local workflow.

Restore.Media charges $4.99, paid once for automatic recovery, billed per file with price varying by repaired file size; it offers a free full-length low-resolution preview and charges for original-resolution download. Consider it when that preview-and-download model fits better than Untrunc’s local repair method.

Fix.Video offers paid one-time file-repair packages, including a 10-file option for $59, paid once with unlimited duration, unlimited file size, and engineer support. It may suit users who prefer a packaged repair service with engineer support over Untrunc’s free reference-based approach.

Kernel Video Repair is a paid desktop alternative for macOS and Windows, priced at $29, paid once for a home license covering two computers; it includes video repair features, no file-size limitation, and a 30-day money-back guarantee. Choose it if those license terms and platform options suit your needs better.

DiskInternals ZIP Repair is a free Windows tool for ZIP files of any size, while Recovery Toolbox File Undelete Free is free for NTFS drives and Remo Repair Word repairs .doc and .docx files for free with no file-size limit on Windows. lzip is another free alternative.

See also Video Repair Software and File Repair Software.

Verdict

Choose Untrunc when a supported MPEG-4 file has a structural fault, you have a matching healthy reference, and you want unlimited, local repair without a fee. Its no-upload workflow and lack of file-size limits are strong advantages, but it is not a general video recovery tool: look elsewhere if the raw media is damaged, the container is unsupported, or you cannot provide the reference clip.