Data Recovery Case File · Cameras, Drones & Cards · Written Last, Missing First

Why an Interrupted Recording Will Not Play

His enquiry was short and describes something very specific. A microSD card that "corrupted while recording a file on an action camera. There is just one file on there but it is corrupted." One file, one interrupted recording, one card. That combination points at a mechanism worth understanding, because it explains why a clip can be almost entirely present and still refuse to open. Video containers write their index at the end — so a recording that stops abruptly leaves all the footage and none of the map, and every player tries to read the map first.

The decode: what the camera never got to write

How a video file is actually built: not in the order it appears. While recording, the camera streams compressed video and audio continuously into the file — that is the bulk of it, and it lands on the card as it is captured. But the structure that describes the recording — where each frame sits, how long it runs, what the frame rate is, how audio aligns with video — is only assembled and written when the recording stops. It has to be, because until then the camera does not know how long the clip will be.

What that means when a recording is interrupted: a flat battery, a knock that unseats the card, a crash or a card removed while running, and the camera never reaches the closing step. So the file on the card contains all the footage recorded up to that instant and no index at all. A player opening it looks for the structure first, finds nothing usable, and reports corruption — which is technically accurate and thoroughly misleading, because the footage is right there, entire and undamaged, with nothing describing it.

Why this is one of the better outcomes: nothing has to be un-deleted or read past damage. The data is present and readable; the job is to build the missing index and wrap it around the stream so a player can navigate it. That is a reconstruction task rather than a recovery from failing media.

How the index is rebuilt, and why a reference clip matters: the parameters needed — resolution, frame rate, encoder settings, audio configuration — are specific to the camera and the mode it was in. The cleanest route is a reference recording from the same camera at the same settings: a short working clip shot deliberately, whose index reveals exactly how that model structures its files. The parameters are lifted from the reference and applied to the orphaned stream. Anyone with the camera still in hand can produce that reference in under a minute, and it materially improves the result.

The one caveat, stated honestly: some cameras buffer the last seconds of footage rather than writing continuously, so the very end of the recording may not have reached the card. The tail is where losses occur; the body of the clip is usually complete.

What not to do: not let anything repair the card, and not run repair tools against the file, since those work by discarding what they cannot parse. And not record anything else on the card, because the stream occupies real space that new footage would overwrite.

On the bench

The card was imaged write-blocked behind the DeepSpar USB Stabilizer 10Gb, and the stream data located and measured on the image — establishing how much footage had actually reached the card before the interruption, which is what determines the length of the recoverable clip. The container index was then reconstructed against a reference recording from the same camera at the same settings, so that resolution, frame rate and audio alignment came from the camera's own structure rather than from assumption. Playback was validated end to end rather than by opening the first frame.

The outcome

The stream measured, the container rebuilt against a matched reference and the clip validated by playing it through. Free assessment, one fixed written figure including VAT, no recovery, no fee. The decode, for anyone with a video file that will not open after an interrupted recording: the footage is almost certainly there — cameras stream video and audio to the card continuously but only write the index describing it when recording stops, because until then the length is unknown; so an interruption leaves the whole clip with no map, and players report corruption because they look for the map first. Keep the camera, shoot a short reference clip at the same settings, and don't let anything repair the file.

Our case files are drawn from genuine enquiries received by our laboratory over the past ten years, anonymised to protect client confidentiality. Each one describes the diagnostic and recovery procedure our engineers apply to that fault, using the equipment listed.