MKV to MP4 converter

OBS and many downloads save MKV, but phones, iMovie, Premiere uploads and most social sites want MP4.

Drop a MKV file hereThe converter loads in your browser.

What happens to your MKV

MKV with H.264/HEVC video and AAC/MP3 audio is remuxed into MP4 without re-encoding. AC-3, DTS, FLAC, Opus or Vorbis audio is converted to AAC while the video stays untouched. Text subtitles can be kept as MP4 timed text; image subtitles (PGS/VobSub) cannot.

Tip: OBS users: remuxing MKV to MP4 is exactly what OBS's own "Remux Recordings" does, and it runs just as fast here.

How to convert MKV to MP4

Drop your MKV file on the box above, or tap it to pick one. The engine (about 31 MB) loads once per visit.
The converter reads the file's streams and shows which codecs are inside.
Keep the defaults, or pick a quality and resolution.
Press the button, wait for the progress bar, then download your MP4.

Prefer the command line?

This is the FFmpeg command the converter runs for a typical MKV (h264 + aac). Paste it into a terminal with FFmpeg installed for batch jobs or files too big for a browser tab:

ffmpeg -y -i input.mkv -map 0:v:0 -map "0:a:0?" -sn -dn -c:v copy -c:a copy -movflags +faststart output.mp4

Streams are copied (-c copy), so this runs at disk speed. Your own file may contain different codecs; the converter above detects them and adapts. For other jobs, ask the FFmpeg command helper.

Questions

Will I lose subtitles?

Text subtitles (SRT, ASS/SSA) are kept as MP4 timed text when "Keep subtitles" is ticked under Advanced; ASS styling is simplified. Image subtitles from Blu-ray (PGS) or DVD (VobSub) cannot be stored in MP4 and are dropped.

How do I convert MKV to MP4 without losing quality?

Leave "Re-encode" unticked. If the MKV holds H.264 or HEVC video, the stream is copied into MP4 untouched, which is lossless and takes seconds.

Can VLC convert MKV to MP4?

Yes, via Media › Convert/Save, but its profiles re-encode the video, which is slow and loses some quality. A remux like this one avoids that.

Is there a file size limit?

We set none. Remuxes stream from disk and work on multi-GB files on a computer; re-encodes are limited by browser memory (about 2 GB of output).

Why did it finish in seconds?

Because nothing was re-encoded. The video packets were copied into a new container.

Is my MKV file uploaded?

No. The MKV is read from your device by FFmpeg running as WebAssembly in the page, and the MP4 is written back to your device. No server ever receives it.

Is there a size limit for MKV to MP4?

We set none. The practical limit is browser memory: roughly 2 GB of output on a computer, and much less on phones.

The formats

MKV	An open container that can hold nearly any codec plus chapters and many subtitle tracks, popular for OBS recordings and archives. Usually: almost anything, plus multiple audio and subtitle tracks
MP4	H.264 + AAC. Plays on almost everything: phones, TVs, browsers, editors, social apps. Written as: H.264 + AAC

Other files to MP4

MKV to other formats

Why some conversions are instant and others take minutes

What happens to each part of an MKV

Swipe the table sideways to see all columns.

Inside your MKV	In the MP4	Speed
H.264 or HEVC video (OBS, most downloads)	Copied unchanged	Seconds
VP9 or AV1 video	Re-encoded to H.264 for Apple compatibility	Minutes (about real time or slower)
AAC or MP3 audio	Copied unchanged	Seconds
AC-3, DTS, FLAC, Opus or Vorbis audio	Converted to AAC (stereo or 5.1 as the source)	Seconds
SRT / ASS / SSA text subtitles	Kept as MP4 timed text (mov_text) when "Keep subtitles" is on; ASS styling is lost	Instant
PGS (Blu-ray) or VobSub (DVD) image subtitles	Dropped: MP4 has no image-subtitle format. Keep the MKV or burn them in with desktop FFmpeg	–
Extra audio tracks (other languages)	The first (default) track is kept	–
Chapters, attachments (fonts, cover art)	Not carried over	–

OBS recordings: why MKV, and how to get MP4

OBS Studio recommends recording to MKV (or its newer hybrid/fragmented MP4) because a plain MP4 is unreadable if recording stops abruptly: the index is written last. An MKV stays playable up to the crash. Afterwards, OBS's own File › Remux Recordings and this page do the same thing: copy the streams into MP4 without re-encoding. Here it also works on a different computer, a Chromebook or a phone, with nothing to install.

OBS multi-track recordings (game audio, mic and Discord on separate tracks) contain several audio streams; the browser converter keeps track 1. To keep them all in MP4, run ffmpeg -i in.mkv -map 0 -c copy out.mp4 on desktop.

MKV to MP4 vs other ways

VLC "Convert/Save": re-encodes by default, which is slower and loses quality even when a lossless remux was possible.
Upload converters: send your whole file to a server and often cap free files at around 1 GB. Here the file never leaves your device and we set no cap.
HandBrake: excellent for re-encoding and HEVC output, but always re-encodes; there is no pass-through remux of video.

See also: MKV vs MP4 compared · MP4 to MKV · MKV to MP3