Free video tool · runs in your browser

MKV to MP4 converter

Q: Will I lose quality converting MKV to MP4?

Auto copies H.264 or H.265 video with AAC or MP3 audio without changing those tracks. If either codec is incompatible, it converts to H.264/AAC. That can lose detail; High quality keeps more than Small file.

Q: Why will my MKV not upload to YouTube or Upstream?

Upstream does not accept MKV uploads. A service can also reject the codecs inside a file. Select Convert to H.264 to make an MP4 with AAC audio, then try uploading again.

Q: Does it keep subtitles and multiple audio tracks?

No. The MP4 keeps only the first video and first audio track. It drops subtitle tracks, other tracks, attachments, chapters and source metadata. Subtitles burned into the picture remain visible.

Q: Can I convert H.265 MKV files?

Yes. Auto can copy H.265 into MP4 if the first audio track is AAC or MP3, or there is no audio. Choose Convert to H.264 for playback on more devices or an upload to Upstream.

Q: Is it free, with no watermark?

Yes. The converter is free. You can download the MP4 without an account or a watermark.

Q: Are my files uploaded?

No. Your browser downloads FFmpeg and runs it on your device through WebAssembly. The video stays on your device during conversion.

Q: Is there a file size limit?

Keep files under 1 GB. A smaller file can still run out of browser memory, particularly on a phone. Test a short clip first. Use a desktop converter for large files.

Convert an MKV to MP4 without uploading it. Copy compatible tracks as they are, or convert to H.264 so more players can open the video.

No sign-up
Free download
No watermark
Files stay on your device

Schedule this video in Upstream. Stream it to YouTube or Twitch at a set time, or keep a playlist running 24/7.

Schedule your video

Drop an MKV file here or Choose a file MKV · files under 1 GB · nothing is uploaded

What is MKV?

MKV is a Matroska container that can hold several video, audio and subtitle tracks. MP4 is also a container, but supports a different set of codecs.

Why convert MKV to MP4?

Upstream does not accept MKV. Convert it to H.264 MP4 before adding it to your library. If the MKV contains H.265, select Convert to H.264: a remux would leave it as H.265.

How to convert MKV to MP4

1
Add your MKV file
Choose an MKV file from your device.
2
Choose a conversion mode
Auto copies tracks that MP4 supports. Select Convert to H.264 if you need a video that plays on more devices.
3
Download the MP4
For H.264 conversion, pick a quality setting. Convert the file and download your MP4.

Conversion settings and limits

Remux or convert

Auto copies H.264 or H.265 video if the first audio track is AAC or MP3, or the file has no audio. It converts other combinations to H.264/AAC. Select Convert to H.264 to re-encode regardless of the source codec.

Quality and file size

The quality settings use CRF 18 for High quality, 23 for Balanced and 28 for Small file. A lower number keeps more detail and usually makes a larger file. These settings have no effect when remuxing.

Audio tracks

Audio is converted to 128 kbps AAC. The converter keeps the first audio track; it does not mix separate tracks. Files without audio stay silent.

Browser memory

The file must be under 1 GB. Your browser needs memory for the source, the output and decoding, so even a smaller file can fail, especially on a phone. Use a desktop converter for long recordings or archives.

Keep the original

Keep the original file. The MP4 has only the first video track; it drops subtitles, extra tracks, attachments, chapters and source metadata.

Video output

Re-encoded video is opaque and 8-bit. An odd width or height may be rounded down by one pixel. The converter does not tone-map HDR or preserve Dolby Vision.

Before you convert an MKV

The file stays on your device

Your browser downloads FFmpeg and runs it on your device through WebAssembly. The video stays on your device during conversion.

Free, with no watermark

The converter is free. You can download the MP4 without an account or a watermark.

Files under 1 GB

Keep files under 1 GB. Smaller files can still run out of browser memory, particularly on phones.

Remux or convert

Copy compatible tracks without re-encoding, or choose H.264 for wider playback support.

When to use it

Convert MKV for your Upstream library.
Copy compatible tracks without re-encoding.
Choose H.264 for wider playback support.

Use it on a 24/7 stream

Download the H.264 MP4 and add it to your Upstream library (see accepted formats and reencoding). Add it to a queue for a 24/7 live stream, or use pre-recorded live streaming for a scheduled broadcast.

FAQ