Batch Convert MKV to MP4 Without Uploading Files

OBS recordings, screen captures, and rips. Turn folders of MKV into MP4 in one pass.

Batch convert MKV to MP4 in one queue
Designed for OBS captures, screen recordings, and longer rips
Local browser processing, no upload, no server timeout
Optional resize and compression in the same pass
Download as individual MP4s or one ZIP

Drop video files here or click to browse

Files queue into the current batch until you convert · MP4, MOV, MKV, WebM, M4V

Overview

The thing about MKV is that almost everything plays it... except the things you actually need to share it with. iPhone Photos refuses to import it, Premiere often will not see it, Windows Media Player ignores it, and most social uploaders reject it outright. The codec inside is usually plain H.264, but the Matroska wrapper is enough to trip up the rest of the pipeline.

Converting MKV to MP4 swaps that wrapper for one almost every consumer tool already understands. Same video, friendlier filename. The most common sources (OBS captures, screen recordings, and most Blu-ray-style rips) convert reliably in this tool, with the caveat that HEVC and HDR variants depend on the browser and machine.

There is no server timeout because there is no server. Long OBS sessions and multi-hour captures process just like short clips, limited only by your device.

Technical notes

Codecs inside MKV

MKV most often wraps H.264, H.265 (HEVC), or VP9 video with AAC, AC3, or Opus audio. The converter decodes the supported video tracks and re-encodes them into H.264 inside MP4 for broad compatibility.

Subtitles and extra tracks

MKV files can contain multiple subtitle and audio tracks, but the MP4 output keeps the primary (first) video and audio track only. Embedded subtitles and additional audio languages or commentary tracks are not carried over.

Long recordings

Multi-hour OBS sessions process fine because nothing is uploaded. The constraint is your device's RAM and disk during encoding, not a server timeout.

Good to know

Primary tracks only

The MP4 output keeps the first video and first audio track. Extra audio languages, commentary tracks, and embedded subtitles are dropped. Keep them as separate .srt or .mkv files if you need them later.

H.265 MKV depends on browser HEVC support

HEVC inside MKV decodes reliably in Safari 16.4+ and recent Chrome/Edge with hardware HEVC. Older or HEVC-less environments may struggle on those specific files; H.264 MKV works almost everywhere.

Very long captures need free disk

Multi-hour captures encode fine but produce large intermediate buffers. Make sure you have free disk and RAM headroom before starting a 4-hour batch.

How to convert MKV to MP4 in bulk

Convert a folder of MKV files to MP4 in your browser without uploading anything.

Add your MKV files

Drag and drop one or many MKV files into the queue, or click to pick them.

Confirm the output preset

Output is preset to MP4. Long OBS captures can be left at the higher quality preset; lower it if you want a smaller upload-ready file.

Start the batch

Click Convert files. Each file is processed locally in your browser.

Download MP4s

Download converted MP4 files individually, or grab the whole batch as a ZIP.

Frequently Asked Questions

Are my MKV files uploaded anywhere?

No. The conversion runs in your browser via WebCodecs and the bytes stay on your device. There is no upload endpoint for video.

Why does VLC play my MKV but Premiere will not import it?

VLC bundles its own decoders. Most consumer editors only accept MP4 with H.264, even when the underlying codec is identical. Converting to MP4 sidesteps the format gate.

Will subtitles or multiple audio tracks survive?

No. The MP4 output contains the primary video and primary audio track only. If you need subtitles, keep them as a separate .srt file alongside the MP4.

Can I convert a 4-hour OBS capture?

In most cases, yes. There is no server-imposed file size or duration cap. The practical limit is the free RAM and disk space on your machine while encoding.

Which browsers does this work in?

Conversion uses the WebCodecs API. Fully supported: desktop Chrome 94+, Edge 94+, Opera 80+, Firefox 130+, and Safari 26+. Safari 16.4 to 25 work for most files but some may fail because their WebCodecs implementation is partial. Browsers without WebCodecs (Chrome/Edge <94, Firefox <130, Safari ≤16.3, Internet Explorer) cannot run the converter at all. Mobile browser support is improving but inconsistent, so a desktop or laptop is recommended for batch work.