My MKV shows no duration and will not seek. Is it damaged?

No. The footage is fine. OBS never wrote the duration or the seek index because it did not reach the end of the recording. Remux the file and both get rebuilt from the clusters that are already there.

Does remuxing lose quality?

No. -c copy moves the encoded frames byte for byte into a new container. There is no decode and no re-encode, so the output is bit-identical video at a fraction of the time a re-encode would take.

Why does OBS default to MKV instead of MP4?

Because of this exact failure mode. OBS warns that recordings to MP4 are unrecoverable if the file cannot be finalised, and points at MKV as the crash-safe choice.

Matroska .mkv · recording recovery

A crash during an MKV recording costs you under a second

Whatever was in the cluster being written — typically well under one second. Every cluster before it is complete and readable on its own.

A crash costs you

Under a second

Index is written

Continuously

Editable directly

Not without a remux

Drop the recording that will not open

Any Matroska .mkv file, however large.

Nothing is uploaded

The check runs entirely in this tab. Your browser reads a few hundred kilobytes of headers from the start and end of the file and never sends any of it anywhere — you can watch the network tab, or turn off your Wi-Fi and run it again.

What you will get back

Which container OBS actually wrote, and whether it writes its index as it goes or only at the end.
How many hours and minutes of footage are still readable, measured from the timestamps inside your file — not estimated from its size.
The exact command that turns it back into a file you can play, and what that command will and will not recover.

Why Matroska behaves this way

Matroska was designed to be streamed, so a reader is expected to arrive mid-file and start decoding. Each cluster carries its own timestamp and enough context to decode from. When OBS dies, the clusters it already flushed are still valid — the file just has no duration and no seek index, which is why a player may show 00:00 and refuse to scrub.

How to get a playable file back

ffmpeg -i broken.mkv -c copy fixed.mp4

This is a remux, not a re-encode: -c copy moves the existing frames into a new container without touching them, so it runs at disk speed and loses no quality. It reads to the end, discovers the real duration, and writes a proper index. OBS ships the same operation as File → Remux Recordings.

Editing .mkv

Premiere and Final Cut do not take MKV directly. Remux first — which you were going to do anyway.

Matroska questions

My MKV shows no duration and will not seek. Is it damaged?: No. The footage is fine. OBS never wrote the duration or the seek index because it did not reach the end of the recording. Remux the file and both get rebuilt from the clusters that are already there.
Does remuxing lose quality?: No. -c copy moves the encoded frames byte for byte into a new container. There is no decode and no re-encode, so the output is bit-identical video at a fraction of the time a re-encode would take.
Why does OBS default to MKV instead of MP4?: Because of this exact failure mode. OBS warns that recordings to MP4 are unrecoverable if the file cannot be finalised, and points at MKV as the crash-safe choice.

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