MKV to MP4 converter

Mostly OBS users. OBS saves recordings as MKV unless you change it, and the file then meets an editor, a phone, a chat app or an upload form that wants MP4. The rest have an MKV from somewhere else, a downloaded film or a camera or capture card, that will not open in QuickTime, Photos, iMovie or a browser. In both cases the picture inside is usually H.264 already, so the job is a change of container rather than a conversion, and it takes about as long as saving the file.

An MP4 keeps its table of contents at the end of the file, written when the recording stops. If OBS crashes, the computer loses power or the disk fills mid-recording, that table is never written and the whole MP4 can be unreadable. An MKV is written so that everything up to the moment it stopped can still be played, which is why OBS recommends it.

So the honest answer for OBS users: OBS can do this conversion itself. File › Remux Recordings takes any MKV it made and writes an MP4 next to it, untouched. Turn on Settings › Advanced › Recording › Automatically remux to mp4 and every recording gets an MP4 copy the moment you stop. Newer versions also offer Hybrid MP4 as a recording format, which aims to be crash-safe and an MP4 at once. This page is for when OBS is not to hand: an MKV someone sent you, a recording on another computer, or a file from a capture card or a downloaded video.

If you are still choosing a recorder, our comparison with OBS covers when OBS is the right tool and when a simpler screen recorder is quicker.

Not every MKV holds AAC. Opus and FLAC are common in files made with free tools, and films usually carry Dolby Digital (AC-3, E-AC-3) or DTS, sometimes as 5.1 surround. QuickTime, iPhones and most editors will not play those inside an MP4, so the page turns that one track into AAC and still copies the picture untouched. Surround sound is mixed down to stereo. That takes longer than a copy, though far less than re-encoding the picture, and the page tells you before you start.

Browsers cannot decode Dolby Digital or DTS on their own. For those, the page downloads a small extra decoder the first time it meets one; like everything else here, it runs on your computer.

Subtitle tracks are left out. MKV can hold almost any subtitle format, MP4 very few, and this page carries none across; it tells you how many are being dropped as soon as you choose the file. To keep them, save them as a separate .srt file first (the ffmpeg steps below show how), and most players will pick up an .srt with the same name as the video.

Newer graphics cards let OBS record HEVC (H.265) or AV1 instead of H.264. HEVC is turned into H.264 by default so the MP4 plays everywhere, which re-encodes the picture and takes longer; tick Keep HEVC as it is to copy it instead, for an MP4 that plays on Apple devices and anywhere else HEVC is supported. AV1 is always re-encoded to H.264, since few editors accept AV1 in an MP4.

If the MKV already plays where it needs to, leave it. VLC, Plex and most smart TVs open MKV, and for an OBS recording you will edit, the MKV is the safer file to keep: it survives a crash and keeps every audio track.

Converting cannot rescue a damaged recording. If the MKV stutters, has a frozen picture or drifting sound, the MP4 will too, and an MKV cut short by a crash converts only as far as it goes. It also cannot burn subtitles into the picture; for that you need an editor or HandBrake.