Convert MKV to MP4 Online — No Upload, No Watermark
MKV is a flexible open container often used for archival and multi-audio-track releases. Converting to MP4 gives you a file that plays on every phone, browser, and editor without re-encoding at playback time.
Drag & drop your video here, or click to browse
Max file size: ~2 GB (memory permitting)
Where MKV files come from
MKV is the container of choice for anything that needs multiple audio tracks and subtitle streams in one file, which is why ripped discs, anime releases and archival encodes use it. It is also what OBS writes by default, because an MKV survives a crash mid-recording.
What changes when you convert MKV to MP4
| Container | Matroska rewritten as MP4 |
|---|---|
| Video | Re-encoded to H.264 at CRF 23 |
| Audio | First audio track re-encoded to AAC |
| Extra tracks | Additional audio tracks and subtitle streams are dropped |
Worth knowing first
MKV routinely carries several audio tracks and a stack of subtitle streams. MP4 supports far less of that, so the conversion keeps the first audio track and drops the rest. If the file has a commentary track or subtitles you need, pull them out before converting: the Subtitle Converter handles the subtitle side.
FAQ
What happens to my subtitle tracks?
They are dropped. MP4 has poor support for the subtitle formats MKV carries, particularly ASS with its styling. If you need the subtitles, either extract them to SRT first, or burn them into the picture with the Subtitle Burner so they survive in any player.
I have English and Japanese audio. Which one is kept?
The first audio track in the file, which is usually but not always the original language. There is no track picker here. If you need the second track, use the FFmpeg Command Generator to build a command with an explicit map, or remux in a desktop tool.
Why does OBS record to MKV instead of MP4?
Because an MP4 is only finalised when recording stops cleanly. If OBS crashes or the machine loses power, the MP4 is unreadable, while an MKV plays right up to the last written frame. The usual workflow is to record MKV for safety and convert to MP4 afterwards, which is exactly this.
Is this MKV to MP4 converter really free and without upload?
Yes. The tool runs entirely in your browser using FFmpeg compiled to WebAssembly. Your MKV file never leaves your device — open the DevTools Network tab to verify zero uploads. No signup and no watermark. The practical size limit is the memory your browser gives this tab, which is generous on a computer and a few hundred megabytes on a phone.