Short answer
Drop the file and IntactFile tells you which of the error's three named causes is yours — wrong extension, unsupported codec, or a corrupt file — then repairs the corruption case by rebuilding a damaged or truncated video container around the footage that survived. 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 (no request carries your video off the device). The honest limit: repair can't add codec support or restore bytes an interrupted copy never wrote, so if the cause is an unsupported codec or a wrong extension, the fix is VLC or a rename, not repair.
Test and repair now
Drop the file above. The diagnosis runs on your machine and answers the two questions this error hinges on: what the file really is, read from its bytes rather than its name, and whether its structure is intact. That tells you in seconds which of the three causes below is yours, and two of the three have free fixes.
Full video repair is rolling out in stages: the structural remux repair (rebuilding a damaged but readable container) runs today, and reconstruction for files whose index was never written is in development. The diagnosis always comes first, and it's always free.
The error names its own three causes
This file isn't playable. That might be because the file type is unsupported, the file extension is incorrect, or the file is corrupt. 0xc10100beCredit where due: the Movies & TV dialog hands you the complete list of suspects. What it doesn't do is investigate. So this page is organized as the error's own three causes, each with the check that confirms it and the fix that follows.
Cause 1: the file extension is wrong
A file's extension is just part of its name. Renaming video.mkv to video.mp4 changes nothing inside, and players that trust the name then choke on the contents. This happens with exported files, downloads renamed in transit, and recovery-tool output. The check: the widget reports the container it finds in the actual bytes. If it says the "MP4" is really something else, the fix is renaming the file back to its true extension — free, ten seconds, no repair involved.
Cause 2: the file type or codec is unsupported
The file is healthy; Windows just can't decode it. Test by opening it in VLC, which carries its own decoders — if it plays there, nothing is broken. Either keep using VLC, or teach Windows the codec: the HEVC Video Extensions from the Microsoft Store covers H.265 from phones, drones, and action cameras, and the AV1 Video Extension covers AV1. Repair has no role in this branch, and a tool that pretends otherwise is selling you something.
Cause 3: the file is corrupt
If the extension is right and even VLC fails, the structure is damaged. With this error that's most often a transfer that didn't finish — phone-to-PC copies and camera card imports are the classic triggers, because an interrupted copy truncates the file and takes its index with it. The footage that arrived is still inside; repair rebuilds the structure around it. That's the case the tool above repairs, in your browser, with nothing uploaded.
What this can and can't fix
The same triage honesty, stated as limits. Repair fixes the file's structure: truncation, broken indexes, mismatched containers. It does not, and should not, touch a healthy file: if the diagnosis finds intact structure, the tool reports that instead of performing a fake repair, and your fix is a codec or a rename. Repair also can't add codec support to your machine, restore footage whose bytes never arrived in an interrupted copy, or open DRM-protected video. If the source file still exists on the phone, camera, or drive it came from, re-copying it is free and worth doing before anything else. A failed repair is never charged.