Repair corrupted video online.
Without uploading it.

Repair corrupted video online, without uploading it

Most "corrupted" videos are not destroyed. A phone, camera or screen recorder writes the audio and video frames to disk as it records, and only at the very end writes a small table of contents, the moov atom (also called the index), that tells a player where every frame is, how long it lasts and which codec settings decode it. If the recording stops before that step (a dead battery, a full card, a crash, the app being killed, a cable pulled during a copy), the frames are on the disk but no player can find them. You get "moov atom not found", error 0xc00d36c4, "this file is not supported", or a file that shows 0:00.

FixMP4 is a video repair tool that runs online, in your browser, without uploading the file. It reads the damaged recording on your own device, finds the frames that survived and writes a fresh, standard index around them. The output is an ordinary MP4, MOV or M4A file that plays in VLC, QuickTime, Windows Media Player, iMovie, Premiere and on your phone.

What "repair corrupted video" really means

Video repair tools tend to promise everything. In practice there are three different situations, and it is worth knowing which one you are in:

1. The index is missing or damaged, the frames are fine. This is by far the most common case: interrupted recordings, files that were never finalized, a header wiped by a bad copy. It is fully repairable, often frame-perfect, and this is what FixMP4 is built for.
2. Part of the media data is damaged. A bad sector or a failed transfer zeroed a few blocks in the middle. The frames around the damage can be saved; the damaged seconds cannot be invented. FixMP4 steps over the damage, keeps audio and video in sync across it and restarts the picture at the next keyframe.
3. The data is gone. A 0-byte file, a file full of zeros, or a recording that was overwritten. No software can repair data that is not there; the only hope is file recovery from the original card before anything else is written to it.

The free preview tells you which situation you are in before you pay anything: if your own repaired file plays on the page, the repair worked.

How the repair works

When you drop a file, FixMP4 first walks its box structure (the building blocks of every MP4 and MOV file) and reports what it finds: a missing index, a truncated media area, a wiped header, or an index that survived but points past the end of the file.

If a usable index survived (for example, a "fast start" file whose end was cut off), it is reused and every frame that is still on disk is kept. If not, the engine rebuilds the index from scratch. It scans the media data and recognizes H.264 and HEVC access units by their NAL unit structure and AAC audio frames by their bitstream syntax. It works out the display order of B-frames from the picture order count and assigns timestamps. For variable frame rate phone recordings it uses the audio clock, so lips stay in sync. Interleaved extras such as timecode or telemetry tracks are stepped over instead of breaking the scan.

The codec settings needed to decode H.264 or HEVC (the SPS and PPS parameter sets) are normally stored only in the lost index. That is why most videos need a reference file: a few seconds recorded with the same device and the same settings. FixMP4 copies only those settings from it, never its content. Audio-only files such as iPhone Voice Memos can usually be repaired without one.

Why it runs in your browser

Video files are personal, large and slow to upload. Desktop repair suites need an install and often a licence before you can see a result. Online services make you upload gigabytes to a stranger's server. FixMP4 avoids both: the engine is JavaScript that runs on your machine, the file is read with the browser's file API and the repaired file is assembled locally. Large files are read in slices instead of being loaded into memory at once, so multi-gigabyte recordings work too. Nothing about your video leaves the device; we only see that someone used the page.

Supported cameras, phones and formats

FixMP4 repairs MP4, MOV, M4A, M4V and 3GP files containing H.264 (AVC) or HEVC (H.265) video and AAC audio. That covers the default recording formats of:

• iPhone and iPad: videos (HEVC or H.264, including 10-bit HDR and portrait rotation) and Voice Memos (AAC).
• Android phones: Samsung, Pixel, Xiaomi and others, including variable frame rate recordings.
• Action cameras and drones: GoPro, DJI, Insta360 single-lens MP4s.
• Cameras: Sony, Canon, Nikon, Panasonic MP4/MOV in H.264 or HEVC.
• Dashcams and CCTV exports that write MP4 or MOV.
• Screen and meeting recorders: OBS (MP4 mode), Zoom, QuickTime, Windows Game Bar.

Not supported yet: ProRes, AV1, VP9, MPEG-4 Part 2 video; PCM, ALAC, Opus and AC-3 audio; fragmented and encrypted (DRM) MP4. MKV files from OBS are a different format and usually still play after a crash; remux them in OBS (File > Remux Recordings).

What to do right now if a video will not play

1. Stop recording to that card or phone. New data can overwrite the frames you want back.
2. Copy the broken file somewhere safe (your computer) and work on the copy.
3. Record a short reference clip with the same device and the same settings (resolution, frame rate, HDR on or off, stabilization). Ten seconds is plenty.
4. Open the repair tool, drop the broken file and the reference, and watch the preview.

If the preview plays, you can download the full file. If it does not, try another reference or read the guide for your device. Nothing is charged in either case.

How FixMP4 compares

Desktop tools such as Stellar Repair for Video and Wondershare Repairit handle many formats and have years of edge cases behind them, but you install software and typically pay before you can save anything. untrunc is free and excellent, but it is a command-line tool you have to build or find a binary for. VLC can play some damaged files and rebuild AVI indexes, but it does not rebuild a missing MP4 index. FixMP4 focuses narrowly on MP4/MOV/M4A with H.264, HEVC and AAC, runs in the browser, and always shows you your own repaired file before asking for money.

Pricing in one sentence

Diagnosis and a 15-second preview are free; exporting full files is $9 per month or $29 per year with unlimited files, and you can cancel in one click from your account.