Slimvid

Preset · MKV to MP4 · stays on device

Convert MKV to MP4 Online

Remux a downloaded 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, MKV, AVI, WMV and 30+ more

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. Remux is instant when the codec already fits.

Processed locally in your browser. Nothing is uploaded.

Processed locally in your browser. Files never leave your device. Up to 1GB — larger files go to the desktop app.

MKV is a wrapper, not a codec

MKV can hold almost anything: H.264, HEVC, VP9, multiple audio tracks. Phones and many editors only want MP4 with H.264 plus AAC.

When the video is already H.264, we remux into MP4 without touching the picture. That is why a 2GB MKV can become an MP4 in seconds.

If the codec cannot live in MP4, we transcode with the hardware encoder. Extra subtitle tracks are not copied — burn them in an editor first if you need them.

What you get

Input
MKV
Output
MP4 (H.264 when transcoding)
Subtitles
Not copied; remux video/audio

Three steps

How to convert MKV to MP4

No sign-up, no upload queue, no watermark. Everything happens 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. Remux is instant when the codec already fits.

Same job, other limits

Related size and platform pages

Convert MOV to MP4 OnlineTurn iPhone and camera MOV files into an MP4 that actually plays in browsers, Discord and slides.MOV → MP4Convert AVI to MP4 OnlineTurn old camera and screen-recorder AVI files into an MP4 that phones and browsers can play.AVI → MP4Convert WebM to MP4 OnlineTurn browser recordings and VP8/VP9 WebM files into MP4 for iPhone, Premiere and chat apps.WebM → MP4Convert MP4 to WebM OnlineMake a web-native WebM from an MP4 for HTML5 pages, Chrome recordings and lightweight embeds.MP4 → WebM

Keep going

Related tools

FAQ

MKV to MP4 FAQ

Desktop app

Files over 1GB? Take it to the desktop.

The browser version is perfect for everyday clips. When you need to crunch big footage or dozens of files, the desktop app does it faster on your own hardware.

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