# Convert MKV to MP4

> Convert MKV to MP4 online free: OBS recordings and downloads become MP4 in seconds, the picture copied with no quality loss. Batch, no upload. No sign-up.

URL: https://nibbo.org/en/mkv-to-mp4/

## MKV

MKV (Matroska) is the container of OBS Studio recordings, many downloads and rips. It can hold almost any codec, plus several sound tracks and subtitles.

OBS records H.264 with AAC unless set otherwise, which fits MP4 as it is. Phones, iMovie, Premiere and most social networks don’t open MKV, which is why it so often becomes MP4.

## MKV to MP4: remux or re-encode

Converting MKV to MP4 is usually a remux: the H.264 or HEVC picture is copied as it is, so the result looks exactly like the original. Sound that MP4 players don’t take (AC-3, PCM) is re-encoded on its own, which takes seconds.

A remuxed file is about the same size as the MKV. A re-encode, or the High, Balanced and Small presets, makes it smaller: a 1080p minute is around 45 MB at High and 30 MB at Balanced.

## How it works

1. Drop one or more MKV files: MP4 is already selected. Quality, maximum resolution and sound can be changed before you start.
2. Streams that fit MP4 are copied; anything else is re-encoded with WebCodecs, or FFmpeg compiled to WebAssembly when the browser can’t.
3. Download each file, or all of them as one ZIP.

## Questions

### Are subtitles and extra sound tracks kept?

The first video and the first sound track are converted. Subtitles and other tracks stay in the MKV.

### Are my videos uploaded?

No. Reading, remuxing and encoding all run in this browser tab. Open DevTools and watch the Network tab while a file converts: no request carries it.

### Why is one file done in seconds and another takes minutes?

A remux only copies the streams, so it runs at disk speed. A re-encode decodes and encodes every frame; FFmpeg in WebAssembly, used when the browser can’t, is slower still.

### How large can a video be?

Up to 3 GB per file for free, and as many files as you like. Remuxes and WebCodecs re-encodes stream from the disk; the FFmpeg path holds the result in memory.

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### Compress video

- [Compress video to a target size](https://nibbo.org/en/compress-video/)
- [Compress MKV video](https://nibbo.org/en/compress-mkv/)
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