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Repair a truncated MP4
A truncated MP4 is a file that ends too early: either the recording stopped before the camera finished writing it, or a copy or download stopped before the end. The two look the same in a player, but they need different fixes.
Recording interrupted, or copy cut off?
| Interrupted recording | Interrupted copy or download | |
|---|---|---|
| Typical cause | Battery died, device crashed, card removed or full | Transfer cancelled, cable disconnected, browser or app closed, disk full |
| Original on the device | Damaged too | Intact |
| File size | Plausible for the recording length | Smaller than the original |
| Fix | Rebuild the missing index (structural repair) | Copy or download again from the source |
If the file transfer was interrupted
When an intact source still exists on a camera, card, phone or cloud account, copy it again and verify the new copy by playing the end of the video. Structural reconstruction should not replace a clean transfer from the original source, because the part that never arrived is not in your copy.
If the recording was interrupted
Phones, action cameras, drones and dashcams write compressed samples continuously while the final movie index is saved at the end. Battery loss, a crash or a forced shutdown can therefore leave the final clip with media data but no usable index. Players see a file of the right size that they cannot read; FFmpeg reports “moov atom not found”.
Some formats keep a partial index while recording, and some cameras try to repair the last clip when switched on again with the same card. If yours offers that, let it try first.
Signs that structural repair is appropriate
- The damaged file is the final clip before the interruption.
- Its size suggests that recording data was written.
- Other clips from the same device and mode play normally.
- Players cannot show duration, seek or identify streams reliably.
How reference-based repair works (and what untrunc does)
The open-source tool untrunc popularized the method: take a healthy MP4 from the same device, learn how it describes the video and audio streams, then scan the truncated file and rebuild an index for the frames found there. It works well when the reference really matches the damaged file: same device, resolution, frame rate, codec and audio settings. It needs a command line and some patience.
FrameRescue follows the same principle in a browser. It analyzes the damaged file itself, uses your reference clip when you provide one, tries compatible structural profiles when you don’t, and decodes the result before offering it.
Preserve the original
Do not edit or overwrite the damaged MP4. Keep a byte-for-byte copy, and keep a short healthy clip from the same settings if one is available. A valid repair should be decoded and checked from beginning to end rather than judged by whether it opens.
Truncated MP4 questions
Can FFmpeg fix a truncated MP4?
Only when the index survived. If the recording was interrupted, the index is usually missing and FFmpeg reports “moov atom not found”. The index has to be rebuilt first; after that FFmpeg can remux or convert the file normally.
Why do repair tools ask for a reference file?
A healthy file from the same device and settings shows how that device describes its video and audio streams. The repair uses it as a model for the missing index. It does not copy any picture or sound from the reference.
What if I don’t have a reference file?
Record a short clip with the same device and the same settings now, if you still have the device. If you don’t, FrameRescue can still try its own structural analysis and compatible profiles.
My truncated MP4 came from a download. Can it be repaired?
Download it again from the source. A file cut off during download is missing data that only the source has; repairing the partial file can at best save the part you already have.
Related repair guides
- Fix “moov atom not found”
What the missing movie index means and why copy or faststart commands don’t rebuild it.
- Repair a corrupted MP4
Phones, action cameras, drones and dashcams: what “corrupted” usually means and what can be recovered.
- Phone died while recording
Does the video save? Where to look on iPhone, Android and cameras, and how to repair the unfinished file.
- Repair a corrupted MOV file
Symptoms, safe first steps and the structural repair path for unplayable MOV recordings.
Repair a truncated MP4
Upload the original damaged file. A healthy clip from the same device is optional. FrameRescue checks the result before offering it, and you pay €5.00 only if a repaired file is ready.