Is the MP4 to MKV converter free?

Yes. Transcodr is free with no accounts, watermarks, or hard limits beyond your device's available memory.

Are my files uploaded to a server?

No. The conversion runs locally via ffmpeg compiled to WebAssembly, so your MP4 file never leaves the browser tab.

Will the video lose quality?

Re-encoding always involves some loss, but you can raise the quality control before converting. MKV uses hevc (Main).

How do I convert MP4 to MKV?

Drop your MP4 file above (or click Browse) — the output is already preset to MKV — then click Convert and download the result.

MP4 → MKV · On-device · No upload

Convert MP4 to MKV

Convert MP4 to MKV in seconds, free and entirely in your browser. MP4 is the universally compatible H.264/AAC container that plays on virtually any device; MKV (Matroska) is a flexible container favoured for high-quality, multi-track video. Transcodr runs real ffmpeg compiled to WebAssembly, so your file is processed on your own device and never uploaded.

Drop files to convert

Video, audio, images, subtitles: anything ffmpeg can read. Drop them anywhere on the page or browse from disk.

Try a sample:

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Time	From		To	Size	Δ	Duration
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MP4 vs MKV

Property	MP4	MKV
Codec	H.264 + AAC	H.265 + AAC
Audio	Yes	Yes
Compatibility	Universal	Desktop players

MP4 → MKV questions

Is the MP4 to MKV converter free?: Yes. Transcodr is free with no accounts, watermarks, or hard limits beyond your device's available memory.
Are my files uploaded to a server?: No. The conversion runs locally via ffmpeg compiled to WebAssembly, so your MP4 file never leaves the browser tab.
Will the video lose quality?: Re-encoding always involves some loss, but you can raise the quality control before converting. MKV uses hevc (Main).
How do I convert MP4 to MKV?: Drop your MP4 file above (or click Browse) — the output is already preset to MKV — then click Convert and download the result.

01 / Engine

Real ffmpeg, compiled to WebAssembly.

Same library Netflix, YouTube, and basically every command-line video tool relies on, running in a Web Worker. Pipe a file in, run a command, pipe bytes back out.

02 / Privacy

Nothing leaves the tab.

No uploads, no accounts, no telemetry beyond an anonymous pageview. We couldn’t see your files if we wanted to — there’s no server in the loop.

03 / Limits

It is, after all, a tab.

Files up to a few hundred megabytes convert comfortably. Beyond that, your browser starts asking pointed questions. Use the desktop ffmpeg for 4K masters.

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