How to use the MKV to MP4 converter
- Drop in one MKV or a whole stack of them.
- Leave the defaults as they are, unless you also want a lower resolution from More settings.
- Press Convert to MP4 and download.
What gets copied and what gets converted
H.264 is native to MP4, so it is copied straight across, and so is AAC sound. Sound in Opus, Vorbis, FLAC, AC-3 or DTS becomes 160 kbps AAC, because many MP4 players cannot handle those formats.
MKVs holding HEVC, VP9 or AV1 picture are encoded to H.264 for compatibility. That is far slower than a rewrap, particularly at 1080p and 4K.
Tracks that are left behind
An MKV can bundle several sound tracks, subtitles, chapters and attached fonts. Only track one of the video and track one of the audio make it into the MP4, so prepare an MKV with the language you want first if it is not the default.
Subtitles are dropped rather than burned into the picture. Hold on to the MKV if you depend on them.
TVs, consoles and USB sticks
Television and games-console media players are dependable with H.264 and AAC in MP4, while their MKV and DTS support varies by model. A TV that shows a picture but plays no sound is often fixed by exactly this conversion.
The index sits at the start of the MP4, which also helps it play smoothly from a NAS or a USB stick.
Questions
Will a copied video look any different?
No. An encoded one, at Balanced, looks very close to the source but is not bit-identical.
How long does a rewrap take?
About as long as reading the file, since no frame is decoded. HEVC or VP9 encodes take many times longer.
Do I need to install anything?
No. MKV files with H.264 can use the browser’s built-in WebCodecs path, and anything else falls back to ffmpeg, which the page downloads once and caches.
Are files uploaded?
No. Reading, copying and encoding all happen inside your browser tab.