About the MKV to MP4
MKV (Matroska) is a flexible container used by many recorders, download tools and media servers, but phones, TVs, editing programs and websites often prefer MP4. This converter turns MKV into MP4 in your browser. When the MKV holds H.264, HEVC or AV1 video and AAC or MP3 sound, which is common, they are copied straight into the MP4 without re-encoding, so it is quick and lossless. Other codecs are re-encoded automatically.
Updated October 2026
How to use the MKV to MP4
- 1Select an MKV file.
- 2Press Convert to MP4.
- 3Wait for the progress bar.
- 4Play the preview.
- 5Download the MP4.
MKV versus MP4
Both are containers. MKV can hold almost any codec, many sound tracks and subtitles; MP4 is more limited but plays on almost every device.
- MKV: flexible, great for media servers
- MP4: universal playback and editing
- Same picture quality when copied
OBS recordings
OBS Studio often records to MKV because it survives crashes. Converting the finished recording to MP4 makes it ready for editing and uploading.
How it works without uploading
Your browser has a built-in video engine (WebCodecs) that phones and computers use to play and record video. This tool uses it through Mediabunny, an open-source media library, to read your file, change it and write a new one, all inside the page. Speed depends on your device: a recent phone or laptop handles a few minutes of HD video comfortably, while long 4K files take longer.
When re-encoding happens
If the MKV holds VP9 video or Opus or Vorbis sound, the tool re-encodes to formats MP4 players expect, which takes longer. The progress bar shows how far it has got.
Checking what is inside an MKV
After you pick the file, the line under its name shows the duration, the resolution and the container. If the conversion re-encodes, the progress bar will move steadily over the whole video; if it copies, it finishes in a few seconds. Either way, the preview lets you check the picture and sound before downloading.
Media servers and smart TVs
Plex, Jellyfin and Kodi play MKV well, but streaming those files to a phone or TV can force the server to transcode. MP4 copies of your files often play directly, which saves server power and avoids stuttering.
Large files on phones
Phones have less memory than computers, so multi-gigabyte MKV files are best converted on a laptop or desktop. Short clips of a few hundred megabytes convert fine on a modern phone.
Phone and computer
Best on a computer for large files; small clips work on phones too. MP4 plays on nearly every device, and there are other video steps. Use MP4 to MOV for Apple software, the Video Compressor to shrink the result, and MOV to MP4 when the container goes the other way.
Features
- Lossless copy when codecs fit
- Re-encodes VP9, Vorbis or Opus when needed
- Large files supported
- Preview before download
- No upload
- No watermark
Frequently asked questions
Is MKV to MP4 lossless?
When the video is H.264, HEVC or AV1 and the sound is AAC or MP3, yes, they are copied. Other codecs are re-encoded at high quality.
What happens to subtitles and extra audio tracks?
The MP4 keeps the main video and the main sound track. Subtitles and additional languages are left out.
Why does my TV play MP4 but not MKV?
Some TVs and phones only support MP4 containers, even when they can decode the video inside. Converting the container fixes that.
Can it handle big files?
Files of a few gigabytes usually work on a computer with enough memory. Phones may struggle with very large files.
Which browsers work best?
Chrome and Edge on computers and Android support the most video formats. Safari 16.4+ and recent Firefox work too, but some codecs, such as HEVC in Firefox, may not be supported there.
Is my video uploaded?
No. It is processed on your own device with your browser's built-in video engine, so private videos never leave your phone or computer.
Can I keep the subtitles?
Not with this tool. Keep the MKV if you need the subtitles, or burn them into the picture with desktop software.