“moov atom not found”: fixing a video that won’t play
You open an MP4 or MOV and get “moov atom not found”, “invalid data found when processing input”, or a player saying the file is damaged. The footage is often still inside the file. What’s missing is the part that tells a player how to read it.
What the moov is
An MP4 or MOV file is made of labelled blocks. The two that matter here:
mdat: the actual video and sound, frame after frame. Usually 99% of the file.moov: the index. It says how big each frame is, where it sits in the file, which frames are keyframes, and how to decode them (resolution, codec settings).
Without the moov, a player has a pile of frames and no way to know where one ends and the next begins, so it gives up.
Why it goes missing
Most cameras and phones write the moov last, when you press stop. If recording ends any other way, it never gets written:
- the battery died or the power was cut mid-recording
- the card was pulled out, or filled up, while recording
- the camera or app crashed or froze
- a copy or download was interrupted, so the file stops before the end
The other common cause is the opposite problem: the moov is fine but the start of the file was damaged or overwritten. Players read the first bytes to recognise the file, so it looks just as broken.
Quick checks first
- Look at the file size. If it’s 0 KB or a few KB, there’s no footage in it to save. Work from the card or drive it came from instead (see below).
- Try VLC. It sometimes plays files other players refuse, though without the index it usually can’t.
- Work on a copy. Keep the original untouched, and if the file is still on the camera card, stop using the card.
If the file came off a card or drive: scan the card
This is usually the best route. The card holds more than the broken file. It often holds other clips from the same camera, and those carry the codec settings the broken one is missing.
Keepsake scans the whole card underneath the files and folders:
- If a
moovexists anywhere on the card, it finds it, works out where the file really starts, checks every frame and rebuilds a playable video with sound. - If the
moovwas never written, it finds the frames themselves (H.264, HEVC and MPEG-4), borrows the settings from your other clips from the same camera, and rebuilds the footage it can verify.
Put the card in a card reader, open Keepsake, pick the card and scan. Previewing is free, so you can see what came back before paying anything.
moov is intact. When the moov was never written, a single file usually doesn’t have enough to rebuild from. Scan the original card if you still have it, or try the free open-source tool untrunc with a good video from the same camera as a reference.What can’t be fixed
If the video data itself was overwritten (the card was reused, or the file is mostly zeros), those frames are gone, and no tool can invent them. What Keepsake can still do is save the parts that survived as clean, playable clips, and show you which moments they cover.