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Convert MP4 to MKV Online for Free

Same video, bigger box. Add the tracks MP4 couldn't hold.

MKV takes almost any number of audio languages, styled subtitles, chapters and even fonts, all in one file. The picture is copied untouched, so it takes seconds. Add extras below to build the file.

holiday-film.mkv · tracks4 tracks

movieVideoH.264 · 1920×1080 · 25 fpscopiedlock

graphic_eqAudio · EnglishAAC stereo · from the MP4copiedlock

record_voice_overAudio · SpanishAC-3 5.1 · dub.ac3addedclose

subtitlesSubtitles · EnglishSRT · plain textaddedclose

add a track

checkSecond languagemicCommentarycheckSRT subtitlesformat_paintStyled subtitlesbookmarksChaptersimageCover art

what happens

boltCopy video and audioThe MP4’s own streams move across bit for bit. No quality change.

add_circleAdd 2 extra tracksMuxed in alongside, each with its language and a default flag.

inventory_2Write the MKV indexSo players can seek instantly and list every track in their menus.

MP44.2 GBMKV4.51 GBtime≈ 28 s

inventory_2Build MKV · 4 tracks

Open MP4, MKV, MOV, AVI, WMV, FLV, RealMedia, DVD VOB, camcorder MTS or almost anything else, and save it as any of 32 formats. The converting happens in this tab. Your video is never uploaded.

video_fileChoose videosscienceMake a 6 s test clip

memoryThe enginenot loaded

whatFFmpeg compiled to WebAssembly

download≈ 31 MB, once per visit

readsloads with the engine

writes32 targets, checked on load

loads when you convert, or nowdownloadLoad now

~/convert

Your files, then one of 32 targets.

Each file is identified from its first bytes as soon as you add it. Once the engine is loaded it is read in full, so you see the real codecs, size and length before you convert.

filefirst bytessizeinside (read by engine)status

movieclose

upload_fileDrop videos hereor click to choose. Any container, any size your device can hold.

Save asreadyno sound trackafter engine loads

Common6 formats

.mp4.avi.mkv.mov.wmv.flv

Web3 formats

.webm.ogv.m4v

Professional5 formats

.mpg.mpeg.vob.mts.m2ts

Mobile2 formats

.3gp.3g2

Legacy4 formats

.rm.rmvb.asf.swf

Codec & camera12 formats

.av1.avchd.divx.f4v.hevc.m2v.mjpeg.mpeg-2.mxf.ts.wtv.xvid

Size

Keep1080p720p480p

Quality

HighBalancedSmall file

Sound

KeepMonoRemove

Frame rate

Keep30 fps24 fps

Length

Whole videoFirst 30 sFirst 10 s

Common · container · since 2001.mp4checked on load

MPEG-4 Part 14 on the ISO base media format. The safest choice when a file has to play anywhere.

file you getvideo.mp4

containermp4

videoH.264 (x264) (if in build)

soundAAC

best forWeb, phones, social, sharing

this browser plays itmaybe

command it runs

ffmpeg -i input.mp4 -map 0:v:0 -map 0:a:0? -vf "scale=trunc(iw/2)*2:trunc(ih/2)*2" -c:v libx264 -preset veryfast -crf 23 -pix_fmt yuv420p -c:a aac -b:a 128k -ac 2 -f mp4 -movflags +faststart video.mp4

no files yetboltConvert to .mp4

Results, read back by the enginefolder_zipDownload all as ZIP

from · downloadDownload

~/chapters

Put named chapters on a long video.

Players like VLC, Plex and Kodi show MKV chapters as a menu and let you skip between them. Click the timeline to drop a chapter mark, or let us place one at every scene change.

0:000:30:001:00:001:30:00

01Opening0:00:00close02Arrival0:31:17close03The market1:04:24close

auto_awesomeAt scene changesClear

~/why-its-instant

Nothing is re-encoded, so nothing is lost.

MP4 and MKV are only containers. Every codec an MP4 can hold also fits in MKV, so we lift the packets out and repack them. It works like moving house: same furniture, bigger rooms. A full re-encode would take far longer and slightly soften the picture.

Remux to MKV (this tool)≈ 25 s

Reads and writes the file once. Limited only by disk speed.

Re-encode to H.264≈ 14 min

What a general converter might do. Slower, and every re-encode loses a little detail.

1 h 32 min · 1080p H.264 · 4.2 GB · typical laptop

~/before-you-switch

MKV is for your library, not for sharing.

Media servers and desktop players love it. Phones, browsers and social apps mostly don't. Keep the MP4 too if you'll send the video to anyone.

dnsPlex & Jellyfincheck_circleFull support, including track and chapter menus.

smart_displayVLC & mpvcheck_circlePlay everything, including styled subtitles.

tvSmart TVscheck_circleMost since about 2015 play MKV from USB. Some ignore ASS styling.

sports_esportsXbox & PlayStationcheck_circleBuilt-in media players handle MKV well.

phone_iphoneiPhone & iPadcancelPhotos and TV apps can’t open it. Third-party players can.

desktop_macQuickTime & iMoviecancelApple’s own Mac apps don’t read MKV.

languageWeb browserscancelChrome plays some MKVs; Safari none. Use MP4 or WebM on the web.

shareSocial & messagingcancelUploads are usually rejected or re-encoded. Send the MP4.

~/other-routes

Back to MP4, or on to something else.

Tools people use alongside this one.

movieMKV to MP4Going back, for phones and sharing. Also a remux in most cases.film.mkvarrow_forwardfilm.mp4 movie_editVideo editorTrim or join clips before packing them into the MKV.clip-1 + clip-2arrow_forwardholiday.mp4 music_videoMP4 to MP3Pull out a soundtrack or commentary as a separate audio file.holiday-film.mp4arrow_forwardsoundtrack.mp3

Sources

[1]Matroska specificationsTracks, chapters and attachments in MKV.Matroska.org ↗[2]Matroska (IETF RFC 9559)The formal standard for the container.IETF ↗[3]MP4 file formatWhat MP4 can and can’t carry.Library of Congress ↗

Frequently Asked Questions

Is converting MP4 to MKV free?

Yes, MP4 to MKV conversion is completely free with no signup, no watermark, and no usage limit. Convert as many files as you need.

Are my files uploaded to a server?

No. The MP4 to MKV converter runs in your browser when your file is supported there, so the file stays on your device for that workflow, reducing server exposure for that workflow. Look at the processing mode before putting anything confidential through it.

How long does MP4 to MKV conversion take?

Most MP4 to MKV conversions finish in under a minute. A large file takes longer in proportion, though the work happens on your machine, so nothing waits on a sign-up.

Will the conversion reduce file quality?

Depends which formats. Lossless in, lossless out, and the file you get back is identical. Convert to something compressed and you trade a little quality for a smaller file, which is usually the trade you wanted.

Does this work on mobile devices?

Yes. The MP4 to MKV converter works on phones, tablets, and desktops in any modern browser including Chrome, Safari, Firefox, and Edge.