If you record with OBS Studio, you have probably seen the advice: record to MKV, because a crash cannot destroy it, then convert it to MP4 for editing. MKV (Matroska) is a sturdy, flexible container, but editors such as iMovie, Final Cut Pro and many phone apps will not open it, Apple's QuickTime Player does not play it, and MKV is not on YouTube's official list of supported upload formats. MP4 is the version everything accepts.
This page converts MKV files to MP4 on our server, with no software to install. It is handy when you are on a different computer from the one with OBS, on a Chromebook, or helping someone who just wants the file to open.
How to convert MKV to MP4
- Drop the MKV onto the box above, or click to choose it. The box shows today's size and length limits.
- Click Convert to MP4. Many browsers cannot preview MKV, so you may see "Your browser cannot preview this file". The server reads it anyway.
- Watch the upload progress, your place in line and the conversion step.
- The MP4 downloads when it is ready. The result screen shows the size before and after, and the server's note tells you whether the streams were copied or re-encoded.
Remux or re-encode
Converting MKV to MP4 is usually a remux: the picture and sound streams move from one container to another, untouched. That is what OBS's own File > Remux Recordings does, and what this converter does when it can.
| Inside the MKV | Result |
|---|---|
| H.264 video (x264, NVENC H.264, QuickSync H.264, AMF H.264) with AAC audio, the most common OBS setup | Remuxed: identical quality, about the same size, fast |
| HEVC or AV1 video (newer OBS encoders), or Opus audio | Re-encoded to H.264 with AAC: very close in quality, may be larger, takes longer; 1440p and 4K come back at 1080p |
| Several audio tracks (game, mic, Discord) | The MP4 keeps the first audio track only |
| Subtitles or chapters (common in downloaded films) | Not carried over |
Warning: If you record with separate audio tracks in OBS (Settings > Output > Recording > Audio Track), this converter keeps only track 1, which is normally the mixed track. If you need every track for editing, use OBS's own Remux Recordings, which keeps all of them.
MKV and MP4 compared
| MKV (Matroska) | MP4 | |
|---|---|---|
| Survives a crash while recording | Yes | Classic MP4 no; Hybrid MP4 in OBS yes |
| Audio tracks | Many, plus subtitles and chapters | Several allowed, but most players and editors use one |
| Opens in iMovie, Final Cut Pro, phone apps | No | Yes |
| Plays in QuickTime and the iPhone Photos app | No | Yes |
| Plays in VLC and most PC media players | Yes | Yes |
Keep MKV as your recording format if it suits you; convert copies to MP4 when a file has to leave your PC.
See what is inside your MKV first
If you want to know before uploading whether the file will be copied or re-encoded, open it in VLC and choose Tools > Codec Information. "H264 - MPEG-4 AVC" with "MPEG AAC Audio" means a fast, lossless remux. "HEVC", "AV1" or "Opus" means the converter will re-encode. The free MediaInfo app shows the same details, including how many audio tracks the file holds.
Why OBS users end up with MKV
A classic MP4 file writes its index when recording stops. If OBS, Windows or the power fails before that, the MP4 is usually unplayable. MKV writes as it goes, so a crash costs you the last few seconds at worst. That is why guides told streamers to record MKV for years.
OBS has since added Hybrid MP4, which is crash-safe like MKV and opens like a normal MP4. In OBS Studio 32.0 (released September 2025) Hybrid MP4 left beta and became the default recording format for new profiles (Hybrid MOV on macOS). Profiles created earlier keep their old setting, so many users still record MKV. Check yours under Settings > Output > Recording > Recording Format. If you do keep MKV, you can tick Settings > Advanced > Recording > Automatically remux to mp4 and OBS will make the MP4 for you after each recording.
This converter is for the files you already have: old recordings, clips a friend sent, or recordings on a computer where OBS is not installed.
Worked examples
A 9 minute gameplay clip for YouTube
An OBS recording at 1080p60 with NVENC H.264 and AAC sound is 1.1 GB as MKV. The converter remuxes it, so the MP4 is also about 1.1 GB with identical quality. Most of the time is the upload. If your upload is slow, cut the highlight first with the video trimmer to send less data.
A tutorial for an editor who uses Final Cut Pro
Final Cut Pro does not import MKV. A 6 minute 1440p tutorial recorded with AV1 converts to an H.264 MP4 at 1080p, which imports straight away. Keep the original MKV if you ever need the full 1440p.
A meeting recording for a colleague's phone
Some meeting and capture tools save MKV. A colleague on an iPhone cannot play it. After conversion the MP4 plays in Photos and Files, and you can shrink it with the video compressor if messaging apps reject the size.
Before you upload a long recording
Recordings are big. At 1080p60, OBS commonly writes several gigabytes per hour, and uploading that much over a home connection takes a long time. Cut the part you actually need first: the video trimmer accepts MKV, and the clip you get back is already an MP4, so you may not need this page at all. For whole streams, remux locally in OBS, which takes seconds and uploads nothing.
Limits and privacy
- One file per job, up to the size and length shown in the drop box. Long streams (hours) are best remuxed in OBS or with ffmpeg on your own computer.
- The upload is deleted when the job ends and the MP4 30 minutes after it is ready. Nothing but the file and the tool name is sent.
- Free use has a daily count shown under the tool.
Other ways to convert MKV to MP4
- OBS Studio: File > Remux Recordings, pick the MKV, click Remux. Keeps all audio tracks. Works only for files OBS can read and only on the computer where OBS is installed.
- ffmpeg:
ffmpeg -i input.mkv -map 0 -c copy output.mp4remuxes and keeps every track, as long as the codecs are allowed in MP4. - VLC: Media > Convert / Save works but always re-encodes, which is slower and loses a little quality.
- HandBrake (free): good for batches and for shrinking files, always re-encodes.
Once the recording is an MP4, the packaging is the next job. AM Jarvis YouTube Studio finds outlier videos in your game or topic and writes titles, descriptions and tags from real YouTube searches.
Troubleshooting
The MP4 has no game sound, only my voice (or the other way round)
Your recording had several audio tracks and track 1 was not the mix. Remux it in OBS to keep all tracks, or set track 1 to your full mix for future recordings.
"This file is too long"
The free tool has a length limit shown in the drop box. Remux long recordings in OBS, or cut the part you need first.
The conversion failed on a recording from a crash
An MKV from a crash usually still converts, missing only the last seconds. If it fails, the file may have no usable video at all; try playing it in VLC.
Audio and picture drift apart
This comes from the recording, often variable frame rate under heavy load. Converting cannot fix it. Lower the recording load or use a constant frame rate in OBS for future sessions.