Is my file uploaded when converting MP4 to MKV?

No. The conversion runs entirely in your browser. The file never leaves your device, there is no server to upload to, and the page works offline once loaded.

Is MP4 to MKV conversion free?

Yes, with no account, no watermark and no file limit per day. frogConvert is open source and there is no server cost to recover, because your device does the work.

How large a file can I convert?

Up to 2 GB for a single file, 500 MB total per batch, and 300 files at once. The practical limit is your device's memory, since everything is processed locally.

Convert MP4 to MKV

Rewraps video into Matroska, which can carry unlimited subtitle and audio tracks.

Convert MP4 to MKV →

Runs on: FFmpeg, compiled to WebAssembly, running in this tab
Steps: Direct, a single conversion
Input: .mp4 · video/mp4
Output: .mkv · video/x-matroska
Uploads: None. The file never leaves your device.

What to expect

Usually lossless rewrapping. MKV is excellent for archiving but poorly supported by hardware players and browsers.

Why convert MP4 without uploading

Most online converters take your file, send it to their servers, convert it there and hand back a download link. That means your document sits on someone else's disk, subject to their retention policy and their breaches. It also means you cannot use them offline, and cannot use them at all for anything confidential.

frogConvert does the conversion in the page itself, with FFmpeg compiled to WebAssembly. There is no upload step because there is no server. You can disconnect from the network and it still works.

About the formats

MP4

The default video container almost everywhere, normally holding H.264 video and AAC audio. Its ubiquity, not its technical merit, is the reason to choose it. More about MP4 files.

MKV

Matroska, an open container that will hold essentially any codec plus unlimited subtitle and audio tracks. Excellent for archiving, less reliably supported by hardware players and browsers. More about MKV files.

Common questions

Is my file uploaded when converting MP4 to MKV?: No. The conversion runs entirely in your browser. The file never leaves your device, there is no server to upload to, and the page works offline once loaded.
Is MP4 to MKV conversion free?: Yes, with no account, no watermark and no file limit per day. frogConvert is open source and there is no server cost to recover, because your device does the work.
How large a file can I convert?: Up to 2 GB for a single file, 500 MB total per batch, and 300 files at once. The practical limit is your device's memory, since everything is processed locally.
What is lost converting MP4 to MKV?: Usually lossless rewrapping. MKV is excellent for archiving but poorly supported by hardware players and browsers.