Swap the video container (MP4, MOV, MKV, WebM) locally - no re-encoding, lossless and no upload.
Running locally on your device ...
0%
Your files never left your device
No. Everything runs in your browser - your file never leaves your device. How this is verifiable
Remuxing only swaps the wrapper of a video file - the container - without recomputing picture and sound. The existing tracks are copied 1:1. This is lossless and many times faster than a real conversion, because nothing is re-encoded. Typical use: store an iPhone MOV as MKV, or repackage an MKV into MP4 so it plays everywhere.
Important and honest: remuxing is NOT editing and NOT transcoding. A pure container swap only works when the target container allows the existing codecs. MP4, MOV and MKV interchange fine for H.264/H.265 and AAC. WebM, however, only allows VP8/VP9/AV1 and Opus/Vorbis - so an H.264 file cannot be remuxed losslessly into WebM. In that case we say so clearly instead of silently re-encoding.
Everything runs locally in the browser with ffmpeg (self-hosted, no third-party CDN). Your video is not uploaded - the decisive difference for private recordings.
| Input formats | MP4, M4V, MOV, MKV, WEBM |
|---|---|
| Output format | MKV |
| Batch processing | No |
| Processing | Locally in your browser (WebAssembly) |
| File upload | None |
Limitations: Remux only, no re-encoding: the codec must fit the target container (H.264/AAC cannot be remuxed into WebM). Picture and sound stay unchanged; no editing takes place. One file per run, ~1 GB limit (4 GB/tab in the browser). All audio and video tracks are preserved.
No. The whole remux happens locally in your browser - even in airplane mode.
No. Remuxing copies the tracks 1:1, nothing is recomputed - it is lossless.
WebM only allows VP8/VP9/AV1 and Opus/Vorbis. An H.264/AAC file does not fit without re-encoding - which we deliberately do not do.
No. This tool only swaps the container. It does not cut, compress or edit anything.
Because nothing is re-encoded - the finished tracks are just copied into a new wrapper. That is many times faster than a real conversion.