OBS crashed and the recording will not play

Why an MP4 dies when OBS does

An MP4 keeps its picture and sound in one large block, and the index describing where every frame sits in a much smaller structure written at the end, when recording stops cleanly. OBS cannot write that index if it is killed first, so you are left with a complete recording and no map. Every player refuses it, which looks identical to the file being destroyed. It is not.

This is also why the file is a sensible size. If it is two gigabytes, there are two gigabytes of video in it.

1. Try OBS's own Remux Recordings first

OBS ships a repair path: File → Remux Recordings. Point it at the broken file and let it write a new one. It costs nothing and is the first thing the OBS forums tell people to do, so try it before anything else.

If you were recording to .mkv or .ts, this will very likely just work: those formats do not depend on a final index, which is exactly why they survive a crash. If you were recording straight to .mp4 and OBS died, remuxing usually cannot help, because the information it would need was never written.

2. Check that the video is still in the file

On a Mac:

ls -l "recording.mp4"
strings -t d "recording.mp4" | grep -m 5 -E 'ftyp|mdat|moov'

ftyp and mdat present with no moov is the good outcome: the recording is intact and only the index is missing. The detail of what that means. A file of a few kilobytes means nothing was ever written to it.

Is your file recoverable? Check it here

This runs in your browser. The file is not uploaded, and only the first and last megabyte are read, which is where the markers that decide the answer live. Works on any computer, including Windows, even though the app itself is Mac only.

This checker has its own page at cinesalve.honorboxx.workers.dev/check — easier to pass to someone else who needs it.

3. Rebuild the index

The index has to be reconstructed, not copied, because it holds the exact byte position and size of every frame in your recording. Doing that needs a healthy file made by the same encoder at the same settings, to know how the frames were written.

untrunc is free and open source and does this, if you are happy compiling a command line tool. Try it before paying anyone. If it will not build on your Mac, these are the errors and what they mean.

Cinesalve

A Mac app that does the same job. Drop in the broken recording and the short clip you just made, and it rebuilds the index so the file plays again. Nothing is uploaded and the recovery runs offline. $69 once, every Mac you own.

OBS writes its MP4s through ffmpeg, which is precisely what this is tested hardest against. Every frame is compared against the original by byte position and size:

Sound comes back with the picture on recordings of this kind, though about one audio frame in ten can land imperfectly and leave a click. The checker above counts what survived before you decide anything.

Make it impossible next time

This is worth two minutes even if you never lose a recording again. Record to MKV, not MP4. In OBS, Settings → Output → Recording, set the format to mkv. MKV does not need a closing index, so a crash costs you nothing but the last second.

Then turn on Automatically remux to mp4 in the same settings, and OBS converts each finished recording for you. You get MP4 files for editing and crash immunity at the same time, which is the setup the OBS community recommends and the reason most long time streamers never see this problem.

If it still will not open

Send it, or just describe it, to cinesalve@proton.me (or the contact form) with the OBS version and the recording settings. You will get a straight answer about whether it can be recovered, including when the answer is no.