H.264 MKV remux finishes in ~20 ms, so the round trip is almost all upload
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The fastest free MKV to MP4 converter online. Drop an MKV file, get a universally playable MP4 back. When the video and audio inside are already H.264 + AAC, native ffmpeg on our server does a stream-copy remux in about 20 ms, with no re-encoding and no quality loss. When audio is FLAC, DTS, or AC3, we transcode just the audio. Up to 500 MB, no signup, no watermark.
Native server-side ffmpeg
Up to 500 MB per file
Fast remux when possible
No watermark
No signup
H.264 / AAC output
Files deleted within 24h
Files are deleted from our server within 24 hours.
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Files upload to our nearest Backblaze B2 storage POP via a presigned URL.
Native server-side ffmpeg: fast remux when possible, full transcode otherwise.
Output is delivered via Bunny CDN and auto-deleted within 24 hours.
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How it works
1
Drop your MKV file
Drag any .mkv file in or click to choose. OBS recordings, Plex / Jellyfin library files, and Matroska archives all work. Up to 500 MB per file.
2
Click Convert to MP4
Native ffmpeg checks the streams inside. H.264 + AAC stream-copies into MP4 with +faststart in about 20 ms, with no quality change. Non-MP4-friendly audio (FLAC, DTS, AC3) is transcoded to AAC; video is still copied untouched.
3
Download your MP4
The finished MP4 is delivered through Bunny CDN. Plays on iMessage, WhatsApp, Slack, Google Slides, and iPhone Photos import, everywhere the original MKV did not.
If you are about to record and you know you will need MP4 at the end, save yourself the round-trip: Clipy records straight to a shareable link with no watermark. No MKV, no conversion step.
Why this is the fastest MKV to MP4 converter on the web
The fast path here is a remux: stream-copying H.264 video and AAC audio from the MKV container into an MP4 container with no re-encoding. Native ffmpeg on a server finishes that in about 20 ms regardless of file size. Browser ffmpeg.wasm tools do the same job 50–100× slower because the file has to ferry through tab memory, and they crash outright on 1 GB+ OBS recordings.
We rebuilt the pipeline. Your file uploads via a presigned URL straight to the nearest Backblaze B2 storage POP, native ffmpeg on our server runs the remux (or a minimal audio-only transcode when needed), and the finished MP4 is delivered through Bunny CDN. For H.264 MKVs, the round-trip time is dominated entirely by upload. The conversion itself is essentially free.
Remux vs re-encode: what actually happens
MKV is just a container. The video and audio streams inside it can already be H.264 and AAC, the exact codecs MP4 expects. When that is the case, native ffmpeg does a remux: strip the MKV wrapper, write the same bits into an MP4 container with +faststart, done. No decoding, no encoding, no quality change.
When the audio is FLAC, DTS, AC3, or another codec that MP4 players reject, we transcode just the audio to AAC at 192 kbps. The video stream is still copied untouched, which is perceptually lossless and much faster than a full re-encode.
Where MKV files come from (and why)
OBS Studio saves screen and game recordings as MKV by default because MKV is recoverable if the recording crashes. MP4 writes its index at the end of the file, so a crash before that step produces an unplayable file. Plex and Jellyfin servers serve in MKV. Anime fansub releases use MKV for multiple audio tracks and subtitle streams. Blu-ray rips keep the MKV wrapper to preserve all the audio. In every case the content is fine. Only the wrapper needs to change.
Common questions
Will my MKV lose quality when converted to MP4?
Almost never. When the inner video codec is H.264, we copy it byte-for-byte into the MP4 container and nothing is re-encoded. Audio is re-encoded to AAC only when the source uses a format MP4 players commonly reject (FLAC, DTS, AC3). That audio step is perceptually lossless at our 192 kbps default.
How long does it take to convert an MKV file to MP4?
For a standard OBS recording with H.264 video, the ffmpeg remux step finishes in about 20 ms regardless of file size, so total time is dominated by upload to the nearest B2 POP. Files with audio that needs re-encoding take slightly longer because ffmpeg has to decode and re-encode the audio track, but the video still goes through at copy speed.
My MKV has multiple audio tracks or subtitles. What happens?
We map the first video and first audio track into the MP4 output. Secondary audio tracks, subtitle streams, and chapter markers are not carried over. MP4 can technically hold them, but most players ignore them. If you need multi-track output, use HandBrake or mkvtoolnix on the desktop.
Is this MKV to MP4 converter really free?
Yes. No signup, no usage cap, no watermark, no paid download gate. The tool is part of Clipy's free toolset because we want people who land here for a one-off conversion to discover that Clipy is the screen recorder they were looking for in the first place.
How big a file can I convert?
Up to 500 MB. Because we run native ffmpeg on the server (not browser ffmpeg.wasm), there is no browser memory ceiling, so large OBS recordings that crash other online converters work here.
Why does OBS save as MKV and not MP4 by default?
MKV is fault-tolerant: if OBS crashes mid-recording, the MKV file is still playable up to the point of the crash. MP4 writes its index at the end of the file, so a crash before that step produces an unplayable file. OBS recommends remuxing to MP4 after recording, which is exactly what this tool does.
Is my file private?
We accept the file over a presigned upload to our B2 storage POP, run the remux on our server with native ffmpeg, and serve the result through Bunny CDN. The source and output are deleted within 24 hours. No signup is required.
Tool not working the way you expect?
Tell us what broke. We resolve every report within 24 hours.
