A video that won’t play after a camera, drone or phone lost power is usually not ruined. MP4 and MOV files keep an index, a table that tells a player where every frame and every bit of sound sits in the file. Most cameras write that index last, when you press stop. If the battery dies, the card fills up or the camera crashes first, the index is never written. The picture and sound are still in the file, often gigabytes of it, but QuickTime has no map to find them and says the file can’t be opened.
That kind of damage can be fixed by rebuilding the index from another clip made by the same camera with the same settings. Damage to the picture itself, such as a card that was partly written over, is different: some of it can be worked around, but nothing can bring back frames that are gone.
First, protect the original
- Copy the file to your Mac and work on the copy. Keep the card as it is.
- If the clip is still on the card, stop recording on it. Every new clip can land on top of the one you’re trying to save.
- If the file shows as 0 bytes or is missing, the card’s file list was never updated. The video data is often still on the card. That is a recovery job, not a repair job: see recovering files from an SD card.
Let the camera try (after you’ve made a copy)
Many cameras check for an unfinished recording when they power on with the card inserted, and close the file themselves. DJI’s manuals say to put the card back, power the camera or drone on and wait about 30 seconds. GoPro cameras show a repair icon and fix the file when you press a button. Some Sony, Canon and Panasonic models offer to restore an interrupted clip too. This works often, not always, and it writes to the card, which is why you copy the card first.
How to tell what’s wrong
| What you see | Likely cause | What helps |
|---|---|---|
| QuickTime says the file can’t be opened; the file is large | Index never written (power loss, full card, crash) | Rebuild the index with a pattern clip |
| The video plays, then freezes, turns green or blocky | Damaged or missing picture data | Try VLC; a pattern clip can’t restore lost frames |
| File is 0 bytes or gone | The card’s file list wasn’t updated | Scan the card with a recovery app |
| Sony card has a .RSV file | Unfinished Sony recording | Reinsert the card in the camera; some models restore it |
| Plays on the camera, not on the Mac | A codec the Mac can’t decode | Not damage: try VLC or the maker’s app |
Try a different player
If the file opens but stutters or breaks up partway, open it in VLC (free). It plays past damaged frames that make QuickTime give up. If VLC shows nothing at all, the index is most likely missing, and no player will help until it’s rebuilt.
Rebuild the video with Reco’s Fix a Video
Reco is a free Mac app, and Fix a Video is one of its tools. It rebuilds MP4 and MOV files whose index is missing. Everything happens on your Mac; nothing is uploaded.
- Open Reco and choose Fix a Video under More ways Reco can help, or from the Tools menu.
- Drop in the video that won’t play. Reco checks it first and tells you what it found: an index that is missing (what it can rebuild), or an index that is intact, which means the damage is in the picture and a pattern clip can’t fix it.
- Pick a pattern clip. This is a video that plays, from the same camera, recorded with the same resolution, frame rate and codec. Reco suggests clips from the same folder. Shoot a few seconds with the same settings if you have none left.
- Choose where to save. Reco writes a repaired copy and leaves the original file unchanged. If the broken clip is on a drive you’re recovering from, the copy has to go on a different drive.
If the repair fails, the most common reason is a pattern clip from a different camera or with different settings. Try another clip. Some cameras record compressed sound that Reco can’t rebuild yet; then the repaired copy plays with picture only, and Reco says so.
If the video was deleted or the card was formatted
Scan the card with Reco instead. When a found video has lost its index, Reco rebuilds it as it recovers, using clips from the same camera that are still on the card. On a Sony FX3 card in our testing, 197 of 199 lost clips came back playable with sound. Results depend on the camera and on how much of the card has been used since.
What can’t be fixed
- Frames that were never written, such as the last second or two before the power went.
- Parts of the card that were recorded over. Those frames are gone; a repair can only leave them out.
- Videos from a card that was fully or low-level formatted in the camera. Those cards read back as empty.
So it doesn’t happen again
- Start long recordings with a charged battery and enough free space on the card.
- Press stop and wait for the card light to go out before you switch off or pull the card.
- Copy footage off the card before you format it, and format it in the camera.
Questions
Why won’t a video play after the camera’s battery died?
Cameras write a video’s index (the part of an MP4 or MOV that tells a player where each frame is) when you stop recording. If the power goes first, the index is never written. The picture and sound are usually still in the file, but QuickTime can’t find them.
Can VLC fix a corrupted MP4 on Mac?
VLC tolerates some damaged frames, and it’s worth a try. It can’t play an MP4 or MOV whose index was never written, because it has nothing to tell it where the frames are. That needs the index rebuilt.
What is a reference or pattern clip?
A video that plays, recorded by the same camera with the same settings (resolution, frame rate, codec). A repair tool reads how that camera lays out its files and uses it to rebuild the broken clip’s index. Clips from another camera or mode usually don’t work.
Is there a free video repair app for Mac?
Yes. Fix a Video in Reco is free, works on the Mac, and uploads nothing. It rebuilds MP4 and MOV files whose index is missing, using a pattern clip from the same camera.