Convert MP4 to MKV
Last updated: June 1, 2026To convert MP4 to MKV, drop your MP4 file into the converter above, then download the MKV result. It's free, needs no sign-up, and there's no watermark. Conversion runs in your browser with on-device FFmpeg, so your files never leave your device.
Why convert MP4 to MKV?
Convert MP4 to MKV free, right in your browser. Because both are containers, our FFmpeg-powered WebAssembly tool can remux your file — copying the existing video and audio streams straight into the open Matroska wrapper without re-encoding — so the result is lossless and finishes fast. MKV then lets you carry unlimited audio tracks, soft subtitles and chapter markers that MP4 handles poorly. Your video never leaves your device, with no upload, sign-up or watermark.
- Building a Plex, Jellyfin or Kodi home-media library — MKV is the de-facto container these servers prefer, and it cleanly stores chapter markers plus multiple language and subtitle tracks for movies and TV episodes.
- Merging extras into one file — you have an MP4 movie and separate subtitle or commentary audio, and you want MKV's open container so a single file holds every soft-subtitle and audio track instead of burning them in.
- Working with codecs MP4 rejects — you need FLAC lossless audio, VobSub/PGS image subtitles, or unusual streams that the MP4 spec won't accept but Matroska happily wraps without conversion.
MP4 vs MKV
MP4 · MPEG-4 Part 14 (H.264)
MP4 with H.264 video is the most universally compatible video format — it plays everywhere and uploads cleanly to YouTube, Instagram, TikTok and messaging apps.
MKV · Matroska Video
MKV (Matroska) is a flexible open container that can hold many video, audio and subtitle tracks in one file. It's popular for archiving, but doesn't play natively in many browsers or on some TVs.
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Convert video to MP4, WebM, MOV, MKV, GIF or MP3.
Open Video ConverterMP4 to MKV — frequently asked questions
Will converting MP4 to MKV reduce the quality?
No. Since MP4 and MKV are both containers, the tool remuxes — it repackages the same compressed H.264/H.265 video and AAC audio into the Matroska wrapper without decoding or re-encoding them. The picture and sound are bit-for-bit identical to the source, and the process is quick because nothing is recompressed.
Will the MKV file be larger than my MP4?
Practically not. A remux keeps the original streams untouched, so the size barely changes — only the lightweight container overhead differs. MKV files are 'bigger' in general only when people deliberately bundle several audio tracks or subtitles into them; a straight one-to-one conversion stays about the same size.
Is the conversion really private and free?
Yes. Everything runs locally through FFmpeg compiled to WebAssembly inside your browser, so the MP4 is never uploaded and never leaves your computer. There is no account, no file-size paywall and no watermark added to the output.
How do I convert MP4 to MKV?
Drop your MP4 file (or several) into the converter, confirm MKV is selected as the output, click convert, then download the MKV file. The whole thing takes a few seconds.
Is this MP4 to MKV converter free?
Yes — it's completely free with no watermark and no sign-up required.
Is it safe to convert MP4 to MKV here?
Yes. Conversion runs on-device with FFmpeg compiled to WebAssembly, so your MP4 file is never uploaded to a server.
Can I convert multiple MP4 files at once?
Convert one MP4 file at a time — finish one, then drop in the next.
Does it work on mobile?
Yes — the converter runs in any modern browser on phones, tablets and desktops.