OBS crashed and my MP4 file is 0 KB or will not open. Is the recording gone?

The recording is usually still there. If the file has a real size on disk, the audio and video are inside it and only the index is missing. Do not record over it and do not let OBS write to that folder again. Copy the file somewhere safe, then rebuild the index with untrunc using a healthy recording made with identical settings as the reference.

Why does ffmpeg say 'moov atom not found'?

That is exactly this failure. ffmpeg is telling you the file has no index. ffmpeg cannot fix it on its own — it needs an index to read the file, and rebuilding one is what untrunc does.

Will recording to MP4 ever be safe?

Not while the index is written last. Switch the container to fragmented MP4 in OBS: same .mp4 extension, same editor compatibility, index written continuously.

MP4 .mp4 · recording recovery

A crash during an MP4 recording costs you the entire file

Everything. Not the last few seconds — all of it. The video and audio are still on disk, but nothing in the file says where they start, how they are encoded, or how long they run.

A crash costs you

The whole recording

Index is written

Once, at the end

Editable directly

Yes

Drop the recording that will not open

Any MP4 .mp4 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 MP4 behaves this way

MP4 was designed for finished files that get downloaded and seeked, so its index describes the whole timeline at once and cannot be written until the timeline is complete. Until you press Stop, the file on disk is a header followed by hours of undescribed bytes. Kill the process and the description never happens.

How to get a playable file back

untrunc -s reference.mp4 broken.mp4

untrunc rebuilds the missing index by copying the structure of a healthy recording. The reference file must come from the same OBS profile — same encoder, same resolution, same audio track layout — because the rebuild assumes the broken file is laid out identically. A reference from different settings produces a file that opens and then plays garbage.

Editing .mp4

Every editor opens MP4 directly. This is the only reason people still record to it.

MP4 questions

OBS crashed and my MP4 file is 0 KB or will not open. Is the recording gone?: The recording is usually still there. If the file has a real size on disk, the audio and video are inside it and only the index is missing. Do not record over it and do not let OBS write to that folder again. Copy the file somewhere safe, then rebuild the index with untrunc using a healthy recording made with identical settings as the reference.
Why does ffmpeg say 'moov atom not found'?: That is exactly this failure. ffmpeg is telling you the file has no index. ffmpeg cannot fix it on its own — it needs an index to read the file, and rebuilding one is what untrunc does.
Will recording to MP4 ever be safe?: Not while the index is written last. Switch the container to fragmented MP4 in OBS: same .mp4 extension, same editor compatibility, index written continuously.

Stop needing this page

The container decides how much you lose. A second copy decides whether it matters.

WeaverClip records fragmented segments and uploads each one while you are still live, verifying byte count and MD5 before anything leaves your disk. Free holds 10 GB for 30 days without a card.

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