MP4 to MKV Converter
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Convert MP4 to MKV online
Convert MP4 to MKV when you want the flexible container — the one media servers, Plex libraries, and archive collections standardise on. Matroska imposes no pixel-format restriction and needs no faststart index, so the stream is written as-is once encoded.
When should you convert MP4 to MKV?
- Add a file to a Plex or Jellyfin library
- Standardise an archive on one container
- Use a format that does not care which codec is inside it
- Prepare a file for a player that handles MKV better than MP4
Before you convert
This re-encodes rather than remuxes
In principle the streams could be copied into the new container in seconds. Every target here uses a fixed encoder profile instead, so the output is predictable — at the cost of encoding time and one generation of quality.
Browsers will not play it
MKV has no native browser support. If the file is going on a web page, stay with MP4 or WebM.
What happens to your file
MP4 to MKV is a full re-encode, not a container swap: the video is decoded and re-compressed with libx264 (H.264) at CRF 23, preset medium, and the audio is re-encoded to AAC at 192 kbps. Matroska has no faststart concept and no pixel-format restriction, so the stream is written as-is once encoded.
Settings this conversion runs with
| Engine | ffmpeg |
|---|---|
| Video codec | libx264 (H.264) |
| Video quality | CRF 23, preset medium |
| Audio codec | AAC |
| Audio bitrate | 192 kbps |
What changes
- The MP4 picture is decoded and re-compressed with libx264 (H.264), so this is a generation loss: the output is built from an already-compressed source, not from the original camera data. Converting MP4 to MKV and back will soften the clip a little more each time.
- Only one video and one audio stream reach the MKV file. Additional audio languages, embedded subtitle tracks, and chapter markers are not carried across.
About MP4 and MKV files
MP4 video
Strengths
- plays almost everywhere
- good quality-to-size
- widely supported
Limitations
- lossy compression
- less flexible than MKV
MKV video
Strengths
- holds many tracks
- flexible container
- high quality
Limitations
- not supported on all devices
MP4 vs MKV
| Format | MP4 | MKV |
|---|---|---|
| Compression | Lossy | Lossy |
| Transparency | — | — |
| Best for | streaming and sharing, playback on any device | high-quality video, multiple audio and subtitle tracks |
Guides for this conversion
- MP4, MKV, MOV, WebM: containers vs codecs
The file extension on a video tells you the container, not how the video is compressed. Understanding the difference explains why some conversions are instant and others take minutes.
Related tools
Frequently asked questions
- Does converting MP4 to MKV re-encode the file?
- MP4 to MKV is a full re-encode, not a container swap: the video is decoded and re-compressed with libx264 (H.264) at CRF 23, preset medium, and the audio is re-encoded to AAC at 192 kbps. Matroska has no faststart concept and no pixel-format restriction, so the stream is written as-is once encoded.
- What should you know before converting MP4 to MKV?
- The MP4 picture is decoded and re-compressed with libx264 (H.264), so this is a generation loss: the output is built from an already-compressed source, not from the original camera data. Converting MP4 to MKV and back will soften the clip a little more each time.
- Is this MP4 to MKV converter free?
- Yes. You can convert MP4 to MKV online for free, with no account and no watermark.
- Do I need to install software or sign up?
- No. Use the converter from your browser without installing software or creating an account. Files are uploaded to our servers for processing.
- Will converting MP4 to MKV reduce quality?
- MKV uses lossy compression, so the file can get smaller while some visual quality may change.
- Are my files safe?
- Yes. Files are processed only to complete the conversion and are auto-deleted after 2 hours. We never share them.