Slimvid

Preset · MKV to MP4 · stays on device

Convert MKV to MP4 Online

MKV is a wrapper that can hold H.264, HEVC, VP9 and several audio tracks. Phones and many editors want MP4 with H.264 and AAC. When the video is already H.264, Slimvid remuxes it without touching the picture. Other codecs are transcoded locally. Subtitle tracks are not copied.

Remux an MKV into MP4 so phones, editors and chat apps will play it.

Drop videos here, or click to browse

Up to 1GB each · MP4, MOV, WebM or MKV

Choose files

Processed locally in your browser. Nothing is uploaded.

Settings

Add a video and the settings for this tool appear here.

How it works

  1. 1Drop the .mkv file.
  2. 2Leave the output on MP4.
  3. 3Convert and download.

Processed locally in your browser. Nothing is uploaded.

Process videos up to 1GB on your device. Nothing is uploaded.

MKV is a wrapper, not a codec

A 2GB MKV of H.264 can become an MP4 in seconds because the picture is copied, not encoded again.

If the codec cannot live in the players you care about, the hardware encoder writes H.264.

Burn subtitles in an editor first if you need them inside the file. This tool does not mux subtitle tracks.

What you get

Input
MKV
Output
MP4
Subtitles
Not copied

The web tier stops at 1GB.

Checked 2026-10-10.

Three steps

How to convert MKV to MP4

Convert MKV to MP4 online for free, no upload. Remux when the codec already fits, otherwise hardware-encode on your device.

  1. 1

    Drop your file

    Drop the .mkv file.

  2. 2

    Choose settings

    Leave the output on MP4.

  3. 3

    Download

    Convert and download.

All compress-video pagesVideo upload limits in 2026

Same job, other limits

Related size and platform pages

Convert MOV to MP4 OnlineTurn iPhone and camera MOV files into an MP4 that plays in browsers, chat apps and slides.MOV to MP4Convert WebM to MP4 OnlineTurn browser recordings into MP4 for iPhone, editors and chat apps.WebM to MP4Convert MP4 to WebM OnlineMake a WebM from an MP4 when a site or HTML5 player asks for one.MP4 to WebMCompress Video for DiscordHit the 20MB free-upload cap without guessing a bitrate. Hardware encoding, nothing uploaded.For DiscordCompress Video to 100MBLand at 100MB for forms that say “maximum 100MB” and for large phone uploads.100MB

Keep going

Related tools

FAQ

MKV to MP4 FAQ

Will I lose quality?
Not on an H.264 remux. Other codecs are re-encoded.
What about subtitles?
They are not copied. Export a burned-in file from your editor if the captions have to travel inside the video.
Is there a size limit?
Process videos up to 1GB on your device. Nothing is uploaded.

Desktop · Coming soon

Desktop · Coming soon

The desktop app is in development. Join the waitlist for launch updates.

Get early accessCompare web vs desktop
  • No file size limit — 4K, hour-long recordings, anything
  • Batch queues: drop a folder, apply one preset
  • Hardware-accelerated encoding (H.264 / H.265)
  • Works fully offline, same privacy guarantee