MKV to MP4 Converter: Convert MKV Files to MP4 Online Free

By the team at VidHaul

MKV (Matroska) is a flexible video container. One MKV file can hold almost any video codec, several audio tracks and several subtitle tracks, which is why it is popular for movies, TV episodes and OBS recordings. The problem is support: iPhones do not play MKV in the Photos app, many smart TVs and car screens skip it, and some video editors refuse to import it. MP4 is the format nearly every device understands. This MKV to MP4 converter turns your MKV into a standard MP4 with H.264 video and AAC sound, right in your browser. You can convert MKV to MP4 free, with no software, no upload, no account and no watermark. Below you will find exactly what the converter does, what happens to audio tracks and subtitles, how big the MP4 will be, how to convert MKV to MP4 on Windows, Mac, Android and iPhone, and when VLC, FFmpeg or OBS remux is the better choice.

How does the MKV to MP4 converter work?

The converter opens the MKV with your browser’s built-in video engine (WebCodecs) and reads every video and audio track in it. Then it checks the video codec. If the video is already H.264, it is copied into the MP4 exactly as it is: no re-encoding, no quality loss, and much faster. If it is HEVC (H.265), VP9, AV1 or another codec, the video is decoded frame by frame and encoded again as H.264 at the same resolution and frame rate, using the encoder’s “medium” quality level. Audio that is already AAC is copied as it is; other audio (Opus, Vorbis, FLAC, MP3) is converted to AAC. Everything is then written into a new MP4 file in your browser’s memory and handed to you as a download.

Worked example (computed from the settings the tool uses): a 10 minute 1080p MKV with HEVC video, so it has to be re-encoded. (With H.264 video inside, the video would simply be copied and keep its original size.) When the browser uses bitrate mode, the “medium” level aims for about 3.2 Mbps of video at 1920x1080. That is 3.2 million bits x 600 seconds / 8, or about 242 MB of video, plus the sound. Where the browser supports constant-quality encoding, it uses a fixed quality step instead (quantizer 29 on H.264’s 0 to 51 scale), and the size then follows the content: calm scenes take less, action scenes more.

How big will the MP4 be?

The MP4 can come out bigger or smaller than the MKV, depending on what is inside the MKV. If the video is H.264 it is copied, so the video part stays the same size. If it has to be re-encoded, this chart shows the video bitrate the converter aims for at common resolutions in bitrate mode, and what that means per minute.

What this means in practice:

• MKV with H.264 inside: the video is copied unchanged, so the MP4 is about the same size as the MKV (a little different only if the sound is converted).
• MKV with HEVC (H.265), VP9 or AV1 inside: these codecs pack more quality into fewer bits than H.264, so the MP4 can be larger than the MKV. That is the price of a file that plays everywhere.
• Need it smaller: run the MP4 through the video compressor, which can aim at a size in MB and lower the resolution.

How to convert MKV to MP4 online for free

1. Choose your file. Click the box at the top of this page or drag and drop the .mkv file onto it.
2. Check the output format. MP4 is selected by default. To pick MOV, MKV or WebM, open “More options” under the box. Formats your browser cannot create are hidden automatically.
3. Press Start. A progress bar shows the percentage done. Keep the tab open; you can cancel at any time.
4. Download the MP4. You see the size before and after. “Copy summary” copies those numbers, and “Convert another file” starts the next one.

There is no account to create, no watermark and no daily limit.

What happens to audio tracks and subtitles?

This is the most important thing to know before you convert a movie.

• Video: copied unchanged if it is already H.264; otherwise converted to H.264 at the same resolution and frame rate.
• Audio tracks: every audio track your browser can decode is kept, in the same order, as AAC. Phones, TVs and most players play the first track by default. To switch languages you need a player that lets you choose the audio track.
• Audio your browser cannot decode: some movie soundtracks use codecs like AC-3 (Dolby Digital) or DTS, which many browsers cannot decode. Those tracks are left out. If it was the only audio track, the MP4 will have no sound, so check the result before you delete the MKV.
• Subtitles: not carried over. Keep the original MKV, or keep a separate subtitle file next to the MP4 for players that support it.
• Chapters: not carried over.

Which output format should you choose?

How to convert MKV to MP4 without losing quality

It depends on the video codec inside your MKV, and the converter picks the right path by itself.

• H.264 video (very common, including most OBS recordings): the video is copied into the MP4 unchanged. This is called a remux: the same video data in a new container, so there is no quality loss at all, and it is much faster than converting. If the sound is AAC too, the whole file is copied.
• HEVC (H.265), VP9 or AV1 video: these do not play everywhere as MP4, so the video is re-encoded to H.264. The resolution and frame rate stay the same and the quality level is balanced, so on a normal screen the MP4 looks very close to the MKV. It is not a bit-for-bit copy, though, and very detailed or grainy footage can look slightly softer.

Not sure which codec your MKV has? Open it in video metadata first. If it says H.264 (AVC), your MP4 will be a lossless copy.

How to remux MKV to MP4 from OBS

OBS can record to MKV, which is safer than MP4 because the recording survives a crash. OBS itself has a “Remux Recordings” option in its File menu that copies an MKV recording into MP4 without re-encoding. Use that when you have OBS open. If you are on another computer or a phone, this page does the same job: an OBS recording in H.264 is remuxed without re-encoding, and one recorded in HEVC or AV1 is converted to a standard H.264 MP4.

Convert MKV to MP4 on Windows, Mac or Linux

Open the page in a current Chrome, Edge, Firefox or Safari. There is no MKV to MP4 converter software to download. A computer is the best choice for long movies because it has more memory and a faster processor than a phone, and many computers have hardware video encoders that the browser can use.

Convert MKV to MP4 on Android or iPhone

Open the page in Chrome or Safari, tap the file box and choose the MKV from Files. It works, but it is slower, and very large files (over about 1.5 GB) may be slow or fail, because the finished MP4 is built in the phone’s memory. Keep the screen on and the tab open while it runs. For a full-length movie, a computer is the better choice.

Is there an MKV to MP4 converter with no limit?

This one sets no file size limit and no daily limit. Searches for “MKV to MP4 converter free 2 GB” or “5 GB” usually come from people who hit an upload cap somewhere else. Because nothing is uploaded here, there is no cap to hit. The real limit is your device’s memory: desktops and laptops handle multi-gigabyte files much better than phones.

VLC, FFmpeg, HandBrake or a browser tool?

• VLC: Media, then Convert / Save lets you convert MKV to MP4 on a computer. It works, but the profile settings can be confusing, and its usual profiles re-encode the video.
• FFmpeg: a command-line tool that can remux (copy) or re-encode. Best for experts and batch jobs.
• HandBrake: a desktop app with many settings, good for re-encoding whole libraries.
• This page: nothing to install, one button, private, works on phones too. Best when you have one or a few files and want a playable MP4 quickly.

Can you convert MKV to MP4 if the browser cannot read it?

No. If your MKV uses a video codec your browser cannot decode (some old or unusual codecs, or HEVC on a system without HEVC support), the page tells you instead of giving you a broken file. Try the latest Chrome or Edge on a computer, or a desktop program. To see which video and audio codecs are inside your MKV before you start, open it in video metadata.

Other formats work the same way: WebM to MP4 for screen recordings and MOV to MP4 for iPhone videos. If you only want the soundtrack, use video to MP3, and to keep one scene, use the video cutter.

How accurate is the MKV to MP4 converter?

• Picture: H.264 video is copied, so it is identical to the original. Other video keeps the same resolution and frame rate but is re-encoded at medium quality, so it is very close to the original but not identical.
• Length and sync: the full file is converted, with sound and picture kept together from start to end.
• Size: can go up or down; HEVC, VP9 and AV1 sources often grow, as explained above.
• Audio: tracks your browser cannot decode (often AC-3 or DTS) are left out, which can leave a movie silent.
• Not kept: subtitles and chapters.
• Limits: long 4K movies need a lot of memory and time; phones may fail on files over about 1.5 GB.

Why this tool is different

Upload-based converters make you send a whole movie over the internet before anything happens, which for a 2 GB file can take longer than the conversion itself, and many cap the file size. This converter reads the MKV straight from your disk and writes the MP4 in your browser tab. You can check it: once the page has fully loaded, turn off your internet and convert a file. It still works.

We also tell you plainly what the converter does to your file: it copies H.264 video without re-encoding, re-encodes other video to H.264, keeps the resolution and frame rate, copies AAC audio, converts other audio, drops subtitles and chapters, and leaves out audio it cannot decode. That way you know before you start whether this tool, a remux, or a desktop program is the right choice.

What we measure

The numbers on this page are computed from the settings in the tool’s code: H.264 video and AAC audio for MP4, a straight copy when the video is already H.264, and for all other video the encoder’s “medium” quality level and the formula that scales bitrate with picture size (about 3.2 Mbps at 1080p in bitrate mode, or quantizer 29 in constant-quality mode). We have not run a public test set of MKV movies, so we do not quote an average size change. The tool itself only reports the size before and after on your screen. It does not collect, log or keep your files.

Sources

• Matroska: Basics (MKV holds many audio, video and subtitle streams)
• Matroska: Element specification (track types and default tracks)
• MDN: Media container formats (MP4 and WebM)
• MDN: Web video codec guide (H.264 is broadly compatible; HEVC support varies)
• MDN: WebCodecs API (the browser video engine the tool uses)

Only convert videos you own or have the right to use.