Moov atom
Also known as: moov atom not found, MP4 index, movie header atom
The index box inside an MP4 or MOV file that tells a player where every frame lives; without it the video data is there but nothing can open it.
Updated
What it means
An MP4 or MOV file is built from boxes, historically called atoms. The mdat box holds the actual audio and video. The moov box holds the map: track types, codecs, durations and a table of where each frame sits inside mdat.
Most cameras write the moov atom last, when recording stops, because only then do they know how long the clip is. That design is efficient and fragile at once.
If power fails, a card pops out or the camera crashes before the stop, the index never gets written. The result is the familiar "moov atom not found" error: a file of the right size that no player will open.
How it works in practice
Some cameras try to rebuild the last clip the next time they boot, so put the battery back and power on before touching the card. On a GoPro Hero 11 or similar body, let that repair finish.
Otherwise, repair tools such as untrunc rebuild a missing index from a healthy reference clip recorded with the same settings on the same camera. The frames are still in mdat; the tool reconstructs the map.
For files meant to stream, FFmpeg can move the moov atom to the front with the faststart option during Remuxing, so playback begins before the whole file arrives.
What to watch out for
Do not keep re-copying a broken file hoping it changes. Copy it once to safety, then work on the copy; some repair attempts rewrite the original.
Uploads and downloads that stop early cut off the end of a file, which is exactly where the index lives. A clip pulled through an interrupted browser download or a half-synced folder from Google Drive link sharing can show the same error as a crash.
A rebuilt file may lose the last seconds or the audio track. Fragmented MP4 (fMP4) recording avoids the problem entirely by writing small indexes as it goes, but few action cameras use it.
How RawClip handles it
A file without its moov atom cannot be read by RawClip either, because no decoder can find the frames. Repair such a clip first, then upload it with the rest. Healthy MP4, MOV, AVI, MKV and M4V files go in exactly as the camera wrote them.