Convert MKV to MP4
Vidmini rewraps your MKV into an MP4 container on your own device. When the video is already H.264 with AAC audio, nothing is re-encoded, so it takes seconds and keeps full quality.
How it works
- 1
Choose or drop your MKV file.
- 2
Keep MP4 as the output format (H.264 video, AAC audio).
- 3
Click MKV to MP4, then download the MP4. Nothing was uploaded.
Why MKV files do not play on your phone or TV
MKV (Matroska) is an open container that can hold almost anything: several audio tracks, subtitles, chapters and many codecs. That flexibility made it popular for screen recordings, OBS captures and video archives. The downside is support: the iPhone Photos app and QuickTime do not open MKV, many smart TVs, car screens and consoles only play some MKV files, and social apps and messengers usually refuse them.
MP4 is the opposite: less flexible, but supported everywhere. Moving the same video into an MP4 container is usually all it takes to make it play on any phone, TV or in any editor.
Copying vs re-encoding: what happens to your MKV
Many MKV files already contain H.264 video and AAC audio, the exact codecs MP4 expects. In that case Vidmini copies the streams into the new container without touching a single frame. This is shown as “Lossless: no re-encoding”: the conversion finishes in seconds, even for long files, and the quality is identical to the original.
If a stream uses another codec, only that stream is re-encoded. HEVC, VP9 or AV1 video becomes H.264; Opus, Vorbis or FLAC audio becomes AAC. This takes longer and depends on your device, but it uses the hardware encoder when available. Surround formats that browsers cannot read, such as AC-3 or DTS, also work: the file is first converted on your device by a built-in fallback, which is slower and downloads a 32 MB converter the first time.
Subtitles and extra tracks
Subtitle tracks stored inside the MKV are not kept in the MP4. If you need them, keep the original MKV or extract the subtitles with another tool before converting. Subtitles that are burned into the picture are part of the video and stay visible.
The MP4 contains one video stream and the audio, which is what phones, TVs and video editors expect. For recordings from OBS or a screen recorder, that is usually exactly what you want: a single file you can edit, share or upload.
Private and fast, even for large files
The conversion runs inside your browser with WebCodecs and WebAssembly. Your MKV is never uploaded, which also means there is no waiting for a multi-gigabyte upload. There is no size limit set by us: the output is streamed to the browser's private storage, so desktop browsers handle files of several gigabytes.
Once converted, Continue with this file sends the MP4 to another tool, for example to compress it for sharing or to trim the start of a recording, without selecting the file again.
Frequently asked questions
Can I just rename .mkv to .mp4?
No. The extension only names the container; renaming does not change the file structure, and most players will refuse the file or play it wrong. The streams have to be written into a real MP4 container, which is what this tool does, often without re-encoding.
Is MKV to MP4 conversion lossless?
When the MKV already contains H.264 video and AAC audio, yes: the streams are copied bit for bit. If the video is HEVC, VP9 or AV1, or the audio uses another codec, that stream is re-encoded, with a small, usually invisible quality loss.
Are subtitles kept?
No. Subtitle tracks from the MKV are not included in the MP4. Subtitles burned into the picture remain visible because they are part of the video itself.
Why did my MKV file fail to open?
Your browser must be able to decode the codecs inside it. H.264, VP8, VP9 and AV1 are widely supported and HEVC works on most recent devices; audio formats it cannot decode, such as AC-3 or DTS, go through a built-in fallback on your device, which is slower, downloads a 32 MB converter the first time and accepts files up to 1 GB. Chrome and Edge usually support the most codecs.
Can I convert OBS recordings?
Yes. OBS can record to MKV because the file survives a crash. Converting it to MP4 afterwards gives a file that every editor and platform accepts, and it is usually lossless because OBS records H.264 with AAC by default.
Is my file uploaded?
No. Everything happens on your device. The page only talks to vidmini.com to load its own code, uses no tracking cookies and keeps working offline once loaded.