Fix it now
- Drop the file
- Repair runs locally
- Download the result
The HERO13 Black records 5.3K60, 4K120 and 2.7K240 into MP4 files, almost always encoded as 10-bit HEVC (H.265) — that's why your filenames start with GX (a GX prefix means HEVC; GH would mean H.264). At high-performance settings the camera gives you no way to fall back to H.264, so nearly every HERO13 clip is HEVC in an MP4 wrapper. When one of those files won't open, the video packets are typically intact and only the moov index is gone. Drop the file above and the tool checks exactly that, in your browser, and rebuilds the container when the footage is recoverable.
How a HERO13 file ends up unplayable
Every MP4 needs a moov atom — the index that maps every frame, its codec configuration, and its timing. The HERO13 writes that index last, when a recording is finalized. Interrupt the camera before that moment and you get a file full of real HEVC footage with no map to it, so players report "unsupported", "corrupt", or just a black frame with no duration.
On an action camera the interruption comes in very specific flavours:
- The battery pops out on impact — a mountain-bike crash, a wipeout, a hard mount knock — and the write stops mid-frame.
- Thermal shutdown. Shooting 5.3K60 or 4K120 runs the HERO13 hot; if it cuts out to protect itself, the current clip is left unfinalized.
- The card is pulled or the camera dies before the recording light stops, so the tail of the file — where the index lives — was never written.
HERO13 footage is also chaptered: long recordings are split into ~12 GB parts on an exFAT card (GX010123.MP4, GX020123.MP4, …), or ~4 GB parts on a smaller FAT32 card. The chapter number is the two digits after GX; the four-digit number that follows is shared across every chapter of the same take. Usually only the final chapter is damaged, and the earlier ones play fine — which is exactly the reference material a rebuild wants.
When SOS fails, and how the rebuild differs
The HERO13 has a built-in recovery step: put the card back in the same camera, power it on, and if it finds an unfinalized clip it shows the SOS repair icon and tries to fix the file itself. Try that first — it's free and it works for minor damage. But SOS only runs on the original camera, only on the raw card, and only for the cases it understands. If the clip already got copied to your computer, if the camera won't recognise it, or if SOS runs and the file still won't play, the on-camera path is exhausted.
That's where a container rebuild comes in. Instead of relying on the camera, it scans the surviving HEVC data and reconstructs the sample tables the HERO13 would have written. Because these files are 10-bit HEVC with a specific frame structure, a healthy clip from the same HERO13 at the same settings (same resolution and framerate) is genuinely valuable: it carries the exact codec configuration the broken file is missing, so the rebuild is faithful instead of a guess. Grab a good GX file with the same four-digit take number, or any normal clip shot in the same mode, and keep it handy — you'll be asked for it only if the file needs it.
Why HERO13 footage shouldn't be uploaded
A HERO13 file is big — a few minutes of 5.3K HEVC runs to gigabytes — and it's often footage you can't reshoot: a race run, a dive, a once-only stunt, a family trip. Upload-based repair sites take a full copy of that onto servers you can't inspect, on a slow round-trip, under terms you didn't write.
Here the repair runs entirely in your browser. The file is read straight from your disk, rebuilt in the tab, and saved back — nothing is transmitted. You can verify it: open your browser's Network tab and watch 0 bytes of the clip leave your machine. That's not a privacy promise, it's the mechanism, and it means even a multi-gigabyte HERO13 clip never has to wait on an upload bar.
What this can and can't fix
Can fix
- The last clip when the battery popped, the camera overheated, or power was cut before finalizing (missing moov)
- Files where the on-camera SOS repair ran but the clip still won't play
- GX…….MP4 chapters copied off the card that open as corrupt or zero-length in every player
- Container damage: broken index, wrong sample offsets, bad timestamps, when the HEVC data itself survived
Can't fix
- Footage physically lost to a failing or counterfeit microSD card — recover the card first, then repair
- Clips already overwritten by loop recording — that data is gone
- A file that reads as 0 bytes or is mostly zeros (nothing to rebuild from)
- Missing HEVC decoder support on your own PC — that's a playback problem, not a corrupt file; install HEVC extensions
If a repair fails, we tell you why (missing data versus broken structure), and you are never charged for a failed repair.