MKV to MP4 converter

FileReshape's MKV to MP4 converter moves the H.264 or H.265 picture of an MKV file into an MP4 without re-encoding, using FFmpeg in your browser, which takes seconds and loses no quality. The file is not uploaded. Other codecs are re-encoded to H.264. Only the first sound track is kept, and subtitles and chapters are not copied.

Drop your MKV file here or click to choose

Did a file not convert correctly? E-mail [email protected], ideally with a small sample file, and it will be fixed.

Key facts

Input: MKV (.mkv). Output: MP4 (.mp4).
Your files are not uploaded: the work is done in your browser, on your own device.
File size: up to 2 GB per file (the limit of the browser's WebAssembly memory).
Needs a current browser (Chrome, Edge, Firefox or Safari) on a computer, tablet or phone; nothing to install.
Free to use, with no sign-up.

MKV to MP4: why convert

MKV (Matroska) files come from OBS Studio, which records to MKV so a crash does not ruin the recording, from TV and satellite recorders, from screen recorders and from video archives. The video inside is usually H.264 or H.265, the same picture an MP4 holds, but iMovie, Premiere, DaVinci Resolve's free version on some systems, PowerPoint, phones, smart TVs and upload forms often refuse the .mkv file. This converter rewraps the video in an MP4 in your browser: the picture is copied unchanged, so a one-hour OBS recording is ready in well under a minute and looks exactly as before. AAC and MP3 sound is copied too; AC-3, DTS, Opus, FLAC and other sound is converted to AAC, which every device plays.

How to convert MKV to MP4

Drop the MKV file in the box, or click to choose it.
Leave "Keep the video as it is" for a fast, lossless conversion, or choose H.264 for older devices.
Click Convert to MP4 and save the MP4 file.

What changes when you convert

OBS recordings

In OBS Studio, File, Remux Recordings does the same thing. This page is handy on a computer without OBS, or when someone sends you an MKV recording. Recordings with several sound tracks (game, microphone, chat) keep only the first track in the MP4.

Subtitles and chapters

MKV files can hold many subtitle tracks and chapters. This tool keeps the picture and the first sound track only. If you need the subtitles, keep the MKV or extract them with a desktop program such as MKVToolNix.

Films with surround sound

AC-3 and DTS sound from films is converted to AAC at 160 kbit/s, so phones and laptops can play it. The channels are kept as far as AAC allows, but the result is not bit-perfect surround for a home cinema.

H.265 and older devices

An MKV with H.265 (HEVC) is copied as HEVC. Recent phones, Macs and Windows 11 play it; for an older TV or PC, choose Convert to H.264, which takes much longer.

About the formats

MKV

MKV (Matroska) is an open, flexible video container. One MKV file can hold one video stream, several sound tracks in different languages, many subtitle tracks and chapters, which is why it is popular for films, recordings from OBS Studio and TV recorders. Phones, iMovie, Premiere and many smart TVs and upload forms do not accept MKV files, even when the video inside is ordinary H.264.

Matroska was started in 2002; the name comes from the Russian nesting dolls (matryoshka).
OBS Studio recommends recording to MKV because a crash does not destroy the whole file.
The video inside is usually H.264, H.265 or VP9 and the sound AAC, AC-3, DTS, Opus or FLAC.
Subtitles can be text (SRT, ASS) or pictures (PGS from Blu-ray discs).

MP4

MP4 (MPEG-4 Part 14) is the most common video file format. Phones, cameras, YouTube, WhatsApp and every computer and TV use it. An MP4 is a container: the picture inside is usually compressed with H.264 or H.265 (HEVC) and the sound with AAC, and the same file can also hold subtitles, chapters and a cover image.

The format was standardised in 2003 and is based on Apple's QuickTime format, which is why MP4 and MOV files are so alike.
H.264 video with AAC sound plays on practically every device made in the last 15 years.
A minute of phone video in 1080p is typically 100–200 MB; in 4K it is often 350–500 MB.
The "faststart" layout puts the index at the beginning, so a video can start playing before it is fully downloaded.

Frequently asked questions

Is my MKV file uploaded?

No. FFmpeg runs inside your browser and reads the file from your own disk in pieces. Large recordings of one or two gigabytes work without any upload.

Why is it so fast?

When the picture is H.264 or H.265, it is copied into the MP4 container byte for byte instead of being decoded and encoded again. Only the file structure changes.

Will the quality change?

Not when the video is kept as it is. If the sound has to be converted to AAC, that step uses a high bit rate and is not noticeable for normal listening.

Can I convert MP4 back to MKV?

This site does not write MKV. Desktop programs such as MKVToolNix or FFmpeg can put an MP4's streams into an MKV without re-encoding.