MP4 to MKV Converter

Remux or convert MP4 videos to MKV — 100% free, forever. No subscriptions, no credits, no file size limits, no sign-up required.
🔒 100% Offline ⚡ Runs in Your Browser ♾ Unlimited Conversions 🚫 No Account Needed
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Drop MP4 Videos Here

Select or drop one or more .mp4 files — converted locally, never uploaded

🔄 Need to do the exact opposite? Try our MKV to MP4 Converter

Free MP4 to MKV Converter — 100% Private & Offline

This MP4 to MKV converter runs entirely inside your browser using WebAssembly. Your video files are never uploaded to any server — all processing happens locally on your device. Your files stay completely private, even without an internet connection after the page loads.

Completely free, no strings attached. There are no subscription plans, no credit systems, no watermarks, no file size caps, and no daily conversion limits. Convert as many MP4 videos as you want, as many times as you want — for free, forever.

Why convert MP4 to MKV? While MP4 is great for broad compatibility, MKV (Matroska) is often preferred for archiving and by media server applications like Plex or Kodi. MKV allows for multiple audio tracks, subtitles, and chapter points that standard MP4 containers can struggle with.

Fast remux or full re-encode. Use "Copy Stream" for an instant, lossless container change that preserves 100% of the original quality. Or choose "Re-encode to AAC" for maximum compatibility with players that don’t support the original audio codec.

Your privacy is guaranteed by design. Because conversion happens entirely offline in your browser, there is no risk of your videos being stored, analyzed, or shared. No account, no email, no tracking — just open the page and convert.

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Frequently Asked Questions

Why would I convert an MP4 to an MKV? +
MKV (Matroska) is a highly flexible container format. Unlike MP4, MKV can store multiple audio tracks (like different languages) and embedded subtitle tracks in a single file, making it the preferred format for movie enthusiasts.
Does the conversion reduce video quality? +
If your MP4 uses standard codecs (like H.264), the tool can perform a 'remux'. This simply extracts the video and audio data and drops it into an MKV container instantly, resulting in zero quality loss.
Can I convert large files without limitations? +
Yes, because the conversion happens directly in your browser without uploading to a server, there are no artificial file size limits. You can convert large video files quickly.