MP4 MKV

MP4 to MKV Converter

Convert MP4 to MKV in your browser. Free, private, and fast. Tune codec, quality, and compatibility without sending files to a server.

This converter runs a full FFmpeg engine in your browser. The first conversion downloads the engine (~31 MB, cached afterwards) — your file itself still never leaves your device.

Drag & drop your MP4 file here

or

Max file size: 50 MB · Your file stays in your browser

Your file is processed locally in your browser — nothing is ever uploaded.

Why Convert MP4 to MKV?

Converting MP4 to MKV is a common task whenever a file has to work somewhere that expects the other format. MP4 is the world's most widely supported video container format. MKV is the open Matroska container that can hold any number of video, audio and subtitle tracks in one file. This converter makes the switch locally in your browser — nothing is uploaded.

Common use cases

  • You have a MP4 file and need it in MKV format.
  • The target software or platform requires MKV but your file is in MP4.
  • Typical use of MKV: Playing OBS recordings on phones, TVs and editors.
  • You want to reduce file size or improve compatibility without using desktop software.
Keep in mind: Only the first video and audio track are converted here, and subtitle tracks are not carried over. Many TVs, phones and editors cannot play MKV directly.

How to Convert MP4 to MKV

  1. Upload or drop your MP4 file into the converter above.
  2. Adjust any output settings for MKV if needed.
  3. Click Convert and download your converted file instantly.

About the Formats

MP4 (MPEG-4 Part 14)

MP4 is the world's most widely supported video container format. It efficiently stores video (H.264 or H.265), audio, and subtitles in a single file with excellent compression.

Compatibility: Universal — supported by every browser, device, operating system, and video platform.

MKV (Matroska Video)

MKV is the open Matroska container that can hold any number of video, audio and subtitle tracks in one file. It is popular for movies, TV recordings and screen captures from tools such as OBS.

Compatibility: VLC, MPV, Plex, Kodi and most desktop players; limited support on iPhone, QuickTime and browsers.

100% Private & Browser-Based

Your files never leave your device. All conversion happens locally in your browser — nothing is uploaded to any server. No sign-up required.

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Need the reverse?

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FAQ

Frequently Asked Questions

Yes — completely free with no sign-up, no watermarks, and no size limits for typical files.

Quality depends on the output settings. For lossless output, choose the highest quality setting available.

Your file is processed entirely within your browser using local JavaScript. It is never uploaded to any server. Only you can access your file.

For browser-based conversion, files up to 50 MB work best. Very large files may take longer depending on your device. We recommend splitting very large files before converting.

Currently, AintoB converts one file at a time to keep the browser-based process simple and private. Reload the page to convert another file.