Repair MKV files that won't play — no upload, nothing to install

Short answer

This tool repairs MKV (Matroska) files whose structure broke — a damaged or missing seeking index, unterminated clusters, a truncated tail that leaves real footage no player can navigate — by rebuilding the container around the video that survived, without re-encoding. It runs entirely in your browser: the file is read on your machine and 0 bytes are uploaded, which you can confirm in the Network tab. It can't bring back footage that isn't in the file — an overwritten stream or a 0-byte file needs recovery, not repair.

Fix your MKV now

1. Drop the file
2. Repair runs locally
3. Download the result

Drop the MKV above. The tool reads it on your machine, tells you what it actually is and whether the structure is intact, then rebuilds the damaged container around the footage that survived — no re-encoding, no quality loss. Nothing is installed and nothing is uploaded. If the file turns out to be healthy and the problem is your player, it tells you that too, instead of "repairing" a file that was never broken.

Why an MKV won't play: how Matroska is built

Matroska isn't built from atoms like an MP4 — it uses EBML, a binary structure of nested elements, each tagged with an ID and its length. Inside one big Segment, the important pieces are theTracks header (which codecs are inside), theClusters that hold the actual compressed frames, aSeekHead that lists where the top-level elements live, and the Cues — the seeking index that maps each timestamp to a byte position in a cluster.

The Cues and the final element sizes are written when a recording or muxfinishes. Interrupt the ending — a dead battery, a crashed recorder, a dropped transfer — and you get a file full of real frames that no player can index: the last cluster has no length terminator, the Cues are missing, and strict players (ffmpeg, Handbrake, most hardware boxes) reject the whole file. That's the repairable case: rebuilding the SeekHead, the Cues, and the element sizes around the surviving clusters is routine work when the frames themselves are still there.

Where broken MKVs come from

Interrupted recordings and captures

OBS, screen recorders, DVR and CCTV boxes, and camcorders often write MKV precisely because it survives interruption better than MP4. But a crash or power loss still leaves the Cues unwritten and the last cluster unterminated. The footage up to the interruption is on disk; the file just has no finished map to it.

Partial transfers and downloads

A copy off a NAS or SD card cut short, an interrupted download, a torrent that never completed its last piece: the result is a truncated MKV. Because the Cues sit at the end of the file, a truncated Matroska typically loses its entire seeking index while keeping most of the video.

Codec confusion — not actually corruption

Sometimes the MKV is fine and one player simply can't decode what's inside — H.265, AV1, or an uncommon audio track. If the file plays in VLC or mpv but fails in a stricter player, that's a codec gap, not damage, and there's nothing to repair. The diagnosis above tells the two apart before you do anything.

What this can and can't fix

A quick sanity check before anything else: a healthy-sized file is a repair candidate; a file far smaller than the footage it should hold usually isn't. The diagnosis above tells you which you have, and a failed repair is never charged.