Compress MKV videos
Shrink MKV recordings and videos into MP4 or WebM, processed on your own device.
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How to compress MKV files
Add your files
Drop files on the box, paste them or choose them from your device. Nothing is uploaded.
Check the settings
The default preset suits most files. Change quality, size or format if you need a smaller file.
Download the result
Save each file or all of them as one ZIP. If a file cannot get smaller, you keep the original.
MKV, the open everything-container
MKV is the file extension of Matroska, an open container format first released in 2002. Its structure (EBML, a kind of binary XML) lets one file hold any number of video, audio and subtitle tracks plus chapters, cover art and attachments such as fonts for styled subtitles. That is why MKV is the usual format for ripped movies and series with several languages, for OBS Studio recordings and for anime releases with typeset subtitles. WebM, the web video format from Google, is a restricted subset of Matroska.
Like MP4, MKV does not determine the quality or size; the codecs inside do. Common combinations are H.264 or H.265 video with AAC, AC-3, DTS or FLAC audio, and SRT or ASS subtitles.
Where the size in an MKV comes from
- High-bitrate video. Blu-ray rips often keep the disc's original bitrate, which can be 20–40 Mbps for a 1080p movie.
- Several audio tracks. Each additional language in 5.1 surround adds several hundred megabytes to a feature film, and lossless audio tracks add far more.
- Game and screen recordings. OBS records to MKV because a crash does not destroy the whole file. Recording settings are tuned for quality and speed, not size, so an hour of 1080p60 gameplay can easily reach many gigabytes.
Subtitles, chapters and fonts are tiny in comparison; removing them saves almost nothing.
What the tool does with MKV files
The tool reads the MKV in your browser and writes an MP4 (H.264 video, AAC audio) or, if you prefer, a WebM (VP9 and Opus). The output carries one video track and one audio track; extra audio languages, subtitle tracks and attachments are not copied, so keep the original MKV if you need them.
| Source | Suggested settings |
|---|---|
| OBS gameplay recording for a clip channel | 1080p, frame rate Keep original (60 looks smoother for games), Balanced |
| OBS recording of a meeting or lesson | 720p or Keep original, frame rate 30, Smallest file |
| Sending part of a recording to a friend | Target size below the messenger's limit, 720p |
| Movie for watching on a tablet | 720p or 1080p, High quality |
Long movies are a heavy job for a browser tab. Processing runs at the speed of your device's video encoder, and the tool refuses files beyond its memory limit instead of failing halfway.
Common problems
- No sound or the wrong language. Only one audio track is used: the one marked as default, otherwise the one with the highest bitrate, and there is no option to pick another. If it is a format the browser cannot decode (DTS and some AC-3 variants), the result has no audio and a note says so. Convert the audio on the desktop or choose an MKV with an AAC or Opus track.
- Burned-in subtitles needed. The tool does not draw subtitles into the picture. Desktop software such as HandBrake can do that.
- The MKV will not open. Browsers decode H.264, VP8, VP9 and AV1 widely, and H.265 only on some devices. An MKV with an older or unusual codec may be rejected with a message.
- Recording was interrupted. MKV files from a crashed recording are usually playable but may lack an index; if the tool cannot read one, remux it first with the "Remux Recordings" option in OBS.
MKV questions
Why convert MKV to MP4?
MP4 plays on more devices, in browsers, on iPhones and in social networks, many of which do not accept MKV uploads. MKV is better for keeping many tracks in one file.
Is MKV better quality than MP4?
No, the container has no effect on quality. A movie in MKV and the same streams in MP4 look identical.
Should I record in MKV or MP4 in OBS?
MKV is the safer choice for recording, because an interrupted MP4 is often unreadable. Convert or compress the MKV afterwards.
Can I keep my subtitles?
Not in the compressed output. If subtitles matter, keep them as a separate SRT file or use a desktop converter that copies subtitle tracks.
More video tools
Go back to the video compressor, or compare with the MP4 and AVI pages. The how it works page describes the browser technology used.