How do I turn on fragmented MP4 in OBS?

Settings → Output → Recording, set Output Mode to Advanced, then pick fragmented MP4 as the Recording Format. The file is still named .mp4 and still opens in your editor.

Is fragmented MP4 bigger than regular MP4?

Marginally. Each fragment repeats a small header, which adds a fraction of a percent over a multi-hour recording. That is the entire price of never losing a recording to a crash.

Does WeaverClip use this?

Yes. The helper records in short fragmented segments and uploads each one as it closes, so a crash can only ever cost the segment in flight — and every segment already in the vault has been verified by byte count and MD5.

Fragmented MP4 .mp4 · recording recovery

A crash during a fragmented MP4 recording costs you one fragment

One fragment — usually a couple of seconds. Every fragment written before it stands on its own and plays.

A crash costs you

One fragment

Index is written

Continuously

Editable directly

Yes

Drop the recording that will not open

Any Fragmented 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 Fragmented MP4 behaves this way

Fragmented MP4 is the container behind HLS and DASH, where a player has to start watching a live stream that has no end yet. That requirement — be readable before the file is finished — is exactly what a crashed recording needs. It is the same .mp4 extension and the same codecs; only the index layout differs.

How to get a playable file back

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

Often unnecessary — most players open a fragmented file as-is. Run the remux when an older editor refuses it, or to consolidate the many fragment indexes into one for faster scrubbing.

Editing .mp4

Opens in editors that take MP4, which is nearly all of them. A remux resolves the rare holdout.

Fragmented MP4 questions

How do I turn on fragmented MP4 in OBS?: Settings → Output → Recording, set Output Mode to Advanced, then pick fragmented MP4 as the Recording Format. The file is still named .mp4 and still opens in your editor.
Is fragmented MP4 bigger than regular MP4?: Marginally. Each fragment repeats a small header, which adds a fraction of a percent over a multi-hour recording. That is the entire price of never losing a recording to a crash.
Does WeaverClip use this?: Yes. The helper records in short fragmented segments and uploads each one as it closes, so a crash can only ever cost the segment in flight — and every segment already in the vault has been verified by byte count and MD5.

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.

Start free — no card How the vault works