Why MKV often needs converting
MKV (Matroska) is a flexible open container that can hold almost any video, audio and subtitle format, with as many tracks as you like. That flexibility is why it’s popular for films and recordings, and also why many devices refuse it: iPhones and iPads, many smart TVs, PlayStation and Xbox media players, and editors like iMovie and Premiere don’t open MKV. MP4 is the format they all accept.
How to use it
- Choose your
.mkvfiles or drop them on the box above. - Wait for the conversion. Copies finish in seconds; re-encodes show a percentage.
- Download the MP4 and check the note: it says whether the video was copied or re-encoded, and whether any audio was left out.
Copy or re-encode?
The converter keeps quality wherever it can:
| Inside the MKV | What happens |
|---|---|
| H.264 video | Copied into the MP4 unchanged: fast and lossless |
| HEVC, VP9, AV1 or VP8 video | Re-encoded to H.264 at high quality |
| AAC audio | Copied unchanged |
| MP3, Opus, Vorbis, FLAC, PCM audio | Converted to AAC |
| AC-3, E-AC-3, DTS, TrueHD audio | Can’t be decoded in a browser: left out |
| Subtitles, chapters, attachments | Not carried over |
The MP4 always uses H.264 video and AAC audio because that’s the one combination every device and website plays.
Checking the result
Play the MP4 before deleting the MKV. In particular, listen for sound and check the language: if the MKV had a commentary track first, that may now be the default audio. Most players let you switch tracks from their audio menu.
Privacy and file size
Your video is converted inside the browser using Mediabunny, an open-source media library, and the browser’s own video codecs. Nothing is uploaded, so there’s no upload wait and no file-size cap from a server. Videos up to about 2 GB work on a computer with enough memory.
Questions
Why did my converted video come out with no sound?
Many MKV files, especially films, use Dolby Digital (AC-3), E-AC-3 or DTS surround audio. Browsers can't decode those formats, so the result note says the video has no sound. A desktop app such as HandBrake or VLC can convert that audio.
Are subtitles kept?
No. MKV subtitles are usually SRT or ASS text, or image-based PGS, which this converter doesn't carry over to MP4. If you need them, keep the subtitle file next to the video, or burn them in with a desktop app.
What about MKV files with several audio languages?
Every audio track that can be converted is kept, so you can still switch language in players that support it. Tracks in formats the browser can't decode are left out, and the note tells you how many.
Does it work with 4K or HDR MKVs?
4K H.264 files are copied fine. 4K HEVC or HDR files need re-encoding, which depends on your browser and graphics chip and can be slow. HDR colour may not be preserved.
Last reviewed 4 November 2026