Why phone and camera recordings get corrupted (and how to prevent it)

By the FixMP4 engineering team · October 3, 2026 · 5 min read

A recording that will not play is rarely random. Almost every case of video or voice memo "corruption" comes down to a handful of causes, and almost all of them share one mechanism: the file never got the chance to be finished. Understanding them helps you prevent the next one and tells you whether the current one can be repaired.

The mechanism: the index is written last

MP4, MOV and M4A files keep their media frames in one part of the file and an index of those frames (the "moov atom") in another. Recorders write the index when you press stop. Anything that ends the recording differently leaves you with a complete set of frames and no index. Players need the index, so the file looks dead, although the content is intact. That is good news: it is the most repairable kind of damage.

Cause 1: the battery died

The classic. Phones and cameras try to stop recordings cleanly when the battery is critically low, but a sudden drop (cold weather, old batteries, power-hungry 4K recording) can cut power before the index is written. Voice Memos recorded overnight or during long lectures are especially exposed.

Prevention: start long recordings above 50%, plug in for anything over an hour, keep spare batteries warm in winter.

Cause 2: the app or device crashed

Camera apps, Voice Memos, OBS and other recorders can crash or be closed by the operating system, for example when memory is low or the device overheats. The recording stops instantly.

Prevention: close other apps before long recordings, keep the system updated, and for OBS record to crash-safe formats (MKV or fragmented MP4) and remux afterwards.

Cause 3: storage ran out

When the card or phone is full, the recorder may not have room to write the index, or it stops at an awkward moment.

Prevention: keep plenty of free space, roughly 400 MB per minute for 4K HEVC video, about 1 MB per minute for compressed voice memos.

Cause 4: overheating

Phones and action cameras protect themselves from heat by shutting down. In the sun, on a dashboard or in a waterproof case, this can happen mid-recording.

Prevention: shade the device, lower resolution or frame rate for long sessions, give it breaks.

Cause 5: the card was removed or the connection was lost

Pulling a card, a loose USB cable on an external recorder or a camera falling and the battery door popping open all stop writing immediately.

Prevention: always stop the recording and wait for the device to finish writing before removing anything.

Cause 6: interrupted copies and downloads

Sometimes the original is fine but the copy is not. An interrupted AirDrop, a cancelled download, a cloud sync that timed out or a USB transfer that failed leaves a file that is cut short. With most MP4s the index is at the end, so it is the part that is missing.

Prevention: verify that copies have the same size as the original before deleting anything from the camera.

Cause 7: storage errors

Failing cards and drives can damage parts of a file. If the damage hits the header, the file looks unreadable even though the rest is fine. If it hits the middle, some frames are lost for good, but the rest can be re-indexed.

Prevention: use quality cards, format them in the camera (not on a computer), and replace them every few years.

What can be saved?

If it already happened

1. Stop using the card or phone storage if the file is not yet copied, to avoid overwriting anything.
2. Copy the broken file to a computer and keep the original untouched.
3. Find a reference: a healthy clip from the same device and settings.
4. Diagnose and preview the repair with the FixMP4 repair tool. It is free to check and runs entirely on your device.

Read more: what the moov atom is and video won't play after recording.

• causes
• battery
• SD cards