Video converter · Windows 10 and 11
Convert MKV to MP4
MKV can hold almost anything, which is exactly why so many phones, TVs and editors turn it away. Octoolo repacks the video into an MP4 without re-encoding whenever it can, so even a multi-gigabyte film is done far sooner than a full conversion, and nothing leaves your computer.
How to convert MKV to MP4
- 1
Start the converter
On Octoolo's home screen, search for convert video and pick Convert video from the results, or open Converters and find it in the list on the left.
- 2
Add your MKV files
Drag in one film or a folder of episodes. Each row lists the length, picture size and video codec, plus the number of sound tracks when there is more than one.
- 3
Choose MP4, keep As it is
Select MP4 and make sure Quality reads As it is. The picture and every sound track MP4 can hold are copied; only the rest is converted.
- 4
Convert and check
Press Convert. Up to four files run side by side, and the line under each one tells you whether its picture was copied or converted.
MKV and MP4 compared
| Detail | MKV | MP4 |
|---|---|---|
| Full name | Matroska Video | MPEG-4 Part 14 |
| Holds | Video, several sound and subtitle tracks, chapters | Video, sound and subtitles |
| Usual video | Any: H.264, HEVC, VP9, AV1… | H.264, H.265 (HEVC) or AV1 |
| Usual sound | Any: AAC, AC3, DTS, Opus, FLAC… | AAC or MP3 |
| Plays in | VLC, Windows 10 and 11, Plex, Kodi; iPhones, many TVs, editors and upload forms do not | Nearly everything: Windows, Mac, iPhone, Android, TVs, browsers, editors and websites |
| Best for | Films with several languages or subtitles, archiving | Sharing, uploading and playing anywhere |
| Since | 2002, open standard | 2003, MPEG (based on Apple's QuickTime) |
Why MKV files need converting
Matroska, the format behind .mkv, is an open container that takes any codec, several sound tracks, subtitles, chapters and even fonts. That flexibility is why MakeMKV saves disc backups in it, and why OBS Studio users often record to it: an MKV recording stays playable if the PC crashes halfway. It is also where several languages, a director's commentary and a handful of subtitle tracks tend to live together in one file.
The same flexibility makes devices hesitate. iPhones and iPads do not play MKV in their own apps, many smart TVs read only some MKVs, and video editors, school portals and upload forms tend to ask for MP4. Windows 10 and 11 and VLC play MKV fine, so the need usually comes when the file has to go somewhere else.
The copy path for big files
Set to As it is, Octoolo leaves the picture alone whenever it is H.264, HEVC, AV1, VP9 or MPEG-4, which covers nearly every MKV. Sound in AAC, MP3, Dolby Digital (AC-3) or Dolby Digital Plus (E-AC-3) goes across as well. Nothing is re-encoded, so the MP4 is about the same size as the MKV and identical in quality, and your graphics card and processor have little to do.
A few MKVs hold older video, such as VC-1 or MPEG-2 from some disc backups. Octoolo does not copy those into an MP4; it converts the picture to H.264 instead, on the graphics card where possible. The same happens if you change the size or the frames a second under More settings. And should a copy fail for any reason, a second attempt converts the file without you doing anything.
Sound tracks and subtitles
| In the MKV | In the MP4 |
|---|---|
| AAC, MP3, AC-3 and E-AC-3 (Dolby Digital and Dolby Digital Plus) | Copied unchanged |
| DTS, Dolby TrueHD, FLAC, PCM | Converted to AAC, same number of channels |
| Text subtitles: SRT, ASS, WebVTT | Kept, as MP4 text subtitles |
| Picture subtitles: Blu-ray PGS, DVD VobSub | Left out: MP4 has no place for them |
Every sound track goes in, so a film with English, French and a commentary still has all three; pick one in your player's audio menu. A 5.1 or 7.1 DTS track becomes 5.1 or 7.1 AAC. MP4 subtitles are simple text, so the words and timing come across but styling made for MKV players may not.
Octoolo cannot turn picture subtitles into text. Keep the MKV for those films, or, if you have the subtitles as an .srt file, the Video Editor can burn them into the picture.
Other ways on Windows
If your MKVs come from OBS Studio, its File › Remux Recordings turns them into MP4 without re-encoding. VLC's Convert / Save and HandBrake also make MP4s, but by default they re-encode the picture, which takes much longer and loses a little detail. FFmpeg on the command line can copy streams if you know its options. Renaming .mkv to .mp4 does not help: the inside of the file stays Matroska.
Octoolo uses that same FFmpeg with the choices made for you. It copies what can be copied, converts only what must be, keeps every sound track, and works through whole folders of episodes while you get on with something else. The progress line shows the speed as a multiple of real time, so you can watch a copy race ahead of the clock.
Octoolo or an online converter?
| Detail | Octoolo | A typical online tool |
|---|---|---|
| Your files | Stay on your computer | Usually uploaded to the site's server |
| Without internet | Works | Does not work |
| File size | No limit | Often capped on free use |
| Many files | Whole folders at once | Often a few at a time |
| Watermarks and ads | None | Common on free plans |
| Cost | $4.99 a month, all 17 apps | Free with limits, or a plan per site |
Questions, answered
Is MKV to MP4 lossless?
The picture is, when it is H.264, HEVC, AV1 or VP9 and you keep As it is: it is copied, not re-encoded. Sound tracks MP4 cannot take, such as DTS, become AAC at a high bit rate.
Why did one film take much longer than the others?
Its picture could not be copied, so it was re-encoded. That happens with older codecs such as VC-1 or MPEG-2, or when you change the size or frame rate; the line under the file shows where the encoding ran.
Where are my subtitles?
Text subtitles are inside the MP4: if they do not show, turn them on in your player's subtitle menu. Picture subtitles from Blu-ray and DVD backups have no place in an MP4, so Octoolo skips them.
Can I keep only one language?
The converter keeps every sound track and drops none; it has no track picker. Players let you choose the track you want from their audio menu, and the extra tracks take little room next to the picture.
Will the MP4 be smaller than the MKV?
About the same when everything is copied. It shrinks a little when big DTS or TrueHD tracks become AAC, and a lot only if you choose Balanced or Small, which re-encode the picture.
Is a 30 GB file a problem?
No. Octoolo works on your own PC, so there is no upload and no size cap; you only need room on the disk for the new MP4. The conversion also keeps going if you switch to another Octoolo app.
MKV to MP4, and 16 more apps.
Download for Windows7 days free, then from $3.99 a month for all 17 apps. Windows 10 and 11.