OBS Studio records in MKV by default. That format survives a crash. MP4 does not. Yet most streaming platforms and editing tools demand MP4. The fix is remuxing, a lossless repackaging of the same audio and video streams. Do it inside OBS for finished recordings. For a obs remux mkv to mp4 job after a crash, repair the MKV first, then remux.
Why OBS Recommends MKV for Recording
MP4 writes its index at the end of the file. If a recording stops short because of a crash, power loss, or other error, that index never gets written. The file becomes unreadable. The audio and video are there, but nothing knows where to find them.
MKV writes its index incrementally, as cues, while the recording runs. A crash leaves the cues incomplete, but almost all your data survives. That makes a obs recording crashed mkv file recoverable. A crashed MP4 is usually gone for good.
How to Remux a Finished OBS Recording
For a completed MKV recording, use the built-in remux tool. It copies the audio and video streams into an MP4 wrapper without re-encoding. No quality loss. The process is fast.
Using the Remux Recordings Menu
Open OBS Studio. Go to File > Remux Recordings. A window opens. Select one or more MKV files, then click Remux. OBS places MP4 copies in the same folder as the originals.
Automating the Remux
Skip the manual step. Go to Settings > Advanced > Recording and enable Automatically remux to mp4 (the exact label varies by version). With this on, OBS creates an MP4 copy the moment you stop a recording.
What Happens When a Recording Crashes
A system crash or unexpected OBS shutdown leaves the MKV file in a broken state. The video and audio data sit inside, but the cues and the final duration are missing or wrong. Players cannot seek through the file. They may report an incorrect total length.
The file is not lost. MKV stores its data in a structure that can be read without a complete index. You can repair the wrapper so the recording becomes usable again.
Remuxing a Crashed MKV Recording
OBS's own remux tool fails on a crashed MKV because the cues are incomplete. Fix the MKV wrapper first. That rebuilds the cues and duration. Then remux the repaired file to MP4.
Follow these steps:
- Copy the crashed MKV file. Work on the copy. Keep the original untouched.
- Use a tool that rebuilds an MKV wrapper by reading the existing data and writing a new, complete cues section. No re-encoding happens.
- Test the rebuilt file. It should play and allow seeking.
- Open OBS Studio. Go to File > Remux Recordings. Select the rebuilt MKV and click Remux.
- OBS produces an MP4 that works in most players and editors.
When OBS Remux Fails and What to Do Next
If OBS still cannot remux a file after a rebuild, the corruption runs deeper. Try the same repair process with a different tool, one more tolerant of missing or broken data. Some utilities handle specific damage patterns better than others.
When a rebuild still fails, the damage has likely reached the audio or video streams themselves, not just the wrapper. Recovery gets harder. You may need to extract the streams individually and mux them into a new file. That work is possible with the right software, though it goes beyond a quick fix.
Preventing Future Crashes
You cannot eliminate crashes. You can reduce them. Keep OBS updated. Do not run other demanding applications while recording. Use a reliable power supply on a desktop, and a battery backup for a laptop. Before a long session or an important recording, test your system stability.
Enable automatic remux in OBS. When a recording completes normally, you get an MP4 right away. When it crashes, the MKV is still there to recover.
Why This Workflow Works
MKV tolerates crashes. Remuxing is fast and lossless. It copies streams without re-encoding. When a crash leaves broken cues, rebuilding the file fixes the seek index and duration. OBS then remuxes to MP4. This sequence rescues most corrupted recordings and keeps you from losing hours of content.