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Convert MP4 to MKV

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Verified by Adam B.· reviewed by FE Editorial ·updated Sep 9, 2026
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Is it possible to convert MP4 to MKV?
Yes - MP4 converts to MKV.

You can do it right here with our free converter - no sign-up, and your file is deleted right after.

The fastest path is a lossless remux with MKVToolNix or FFmpeg, which copies all streams into the MKV container in seconds with no quality loss. Our free converter above handles it automatically and deletes your file after converting. Only use HandBrake if you also want to change the codec or bitrate.

Also to MKV: USM · TP · MPEG4

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Tested on macOS, Windows & Linux
Last verified Sep 2026

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Why convert MP4 to MKV?

People switch from MP4 to .MKV mainly to gain full subtitle support - MKV handles image-based PGS and VobSub tracks that MP4 cannot store properly. MKV also carries multiple audio tracks and chapter markers with fewer restrictions, making it the standard container for archival rips and Blu-ray remuxes.

How to convert MP4 to MKV

MKVToolNix OPEN-SOURCE

Add your MP4 in MKVMerge GUI, set the output filename to .mkv, and click Start multiplexing - the remux takes seconds with no re-encoding.

HandBrake FREE

Open your MP4, set Format to MKV in the Summary tab, then start the encode - use this only if you also need to change the codec or resolution.

Command line - FFmpeg CLI

Run ffmpeg -i in.mp4 -c copy out.mkv to remux instantly without re-encoding.

Programs that convert MP4

Miro Video Converter
HandBrake
Any Video Converter FREE
AviDemux
ConvertXtoDVD
Free Studio
Freemake Video Converter
MediaCoder

About these formats

.MP4 MPEG-4 Part 14 Video File

An MP4 file is a video container (MPEG-4 Part 14, standardized 2003) that holds video, audio, subtitles, and chapters in one file. It plays on every phone, computer, browser, and smart TV…

Open .MP4 details →
.MKV Matroska Video

An MKV file is a Matroska multimedia container that holds video, multiple audio tracks, subtitles and chapters in one file. Open it for free with VLC media player, or on Windows 11 with the…

Open .MKV details →

Quality & what to watch

  • Remuxing with MKVToolNix or FFmpeg (-c copy) is lossless - quality is unchanged and file size differs by under 1%.
  • HandBrake always re-encodes, which reduces quality and takes much longer; avoid it for a simple container swap.
  • MKV is not universally supported - some smart TVs and phones that play MP4 may not accept MKV, so test before deleting the original.

Frequently asked questions

Does converting MP4 to MKV reduce quality?
No, not when remuxing with MKVToolNix or FFmpeg -c copy; the encoded data is copied byte-for-byte. Only HandBrake reduces quality because it re-encodes.
Why is the MKV almost the same size as my MP4?
Because the video and audio data is identical - only the container wrapper changed. A small size difference (under 1%) comes from MKV header overhead.
Can I add subtitles during the conversion?
Yes - in MKVToolNix, add your MP4 and subtitle file (.srt, .ass, etc.) together before multiplexing. FFmpeg also accepts multiple inputs in a single command.
Will MKV play on my TV or phone?
MKV is widely supported on desktop players like VLC and many smart TVs, but not universally. Test playback before deleting your original MP4.