OBS MKV to MP4 — stream-copy remux
OBS records MKV for crash safety. Premiere, Resolve, YouTube and TikTok want MP4. Drop your OBS recording here for an instant remux — no re-encode, no quality loss, no upload.
drop an OBS .mkv here
or click to choose
Why OBS records to MKV, not MP4
MP4 is a closed container — the index (moov atom) gets written at the end of recording. If OBS or your machine crashes before that final write, the MP4 is unplayable. MKV writes its index continuously, so a crashed MKV is still usable.
Official OBS guidance: record to MKV, remux to MP4 after the session for editing or uploading. The OBS UI has "Automatically remux to MP4" but it only fires after a successful session — not retroactively. This page handles the retroactive case.
Remux vs convert — the difference matters
- Remux — swaps the MKV wrapper for an MP4 wrapper. The video and audio bytes don't change. Output is bit-identical. Takes seconds, not minutes.
- Convert / re-encode — runs the video through the encoder again. Adds quality loss. Slow.
For OBS recordings (which are usually H.264 or H.265 video + AAC audio), remux is always what you want. There's nothing to gain from re-encoding except smaller files — and if you want that, use our compress tool after remuxing.
Why we can do a 10 GB remux in seconds
FFmpeg's -c copy flag copies streams without decoding or re-encoding. The CPU isn't doing video math; it's just relabeling bytes. The bottleneck becomes disk I/O. In a browser, that means how fast WebAssembly can write the output file to memory — usually a few hundred MB/sec.
Long stream / gameplay recordings — under 2 GB
WebAssembly memory caps around 2–4 GB. A 1-hour 1080p60 OBS recording at 12 Mbps is ~5 GB, which won't fit. Two workarounds:
- Split the recording before remuxing, then remux each part.
- Use desktop OBS's built-in remuxer (File → Remux Recordings) for files over 2 GB.
Privacy — gameplay and screen recordings
Gameplay clips often include your username, voice chat, things you didn't realize were on screen. Online remuxers upload your file to a server. Here, the file stays on disk — the only thing that crosses the network is this page itself.
FAQ
Will the remux change my video quality?
No. Stream-copy is bit-identical. Frame-by-frame the output is the same as the input.
How long does a 5 GB OBS recording take to remux?
If it fits in WebAssembly memory, under a minute. The bottleneck is browser memory, not CPU.
OBS records VP9 / AV1 to MKV. Will those remux to MP4?
MP4 officially supports AV1; VP9 in MP4 is also widely supported. Both should remux cleanly. If a particular player rejects the output, re-encode with our convert tool.
My recording has multiple audio tracks (game + mic). Does it keep both?
Yes — all tracks are copied. MP4 supports multiple audio streams.
What if my MKV has a corrupted footer?
FFmpeg usually recovers MKV cleanly because MKV indexes continuously. If remux fails, the file is genuinely broken — try OBS's own "Recover MP4 Recordings" tool or untrunc.
Can I do this for multiple files?
One at a time on this page. Drop the next file when the first finishes.
Does the file get uploaded anywhere?
No. Cut your internet after loading the page — the remux still works.