How to convert MKV to MP4
- Choose one or more MKV files.
- Keep Format on MP4 and Video codec on Automatic (copy when possible).
- Select Convert to MP4.
- Read the file list to see what was copied, then download.
Worked example
An MKV with H.264 video and AAC sound becomes an MP4 with both tracks copied; the file list shows H.264 (AVC) (copied, not re-encoded) and AAC (copied). The converter's automated test checks this copy path with a MOV file, and ffprobe reads the result as H.264 with AAC.
Formats and limits
| Input | MKV |
|---|---|
| Output | MP4 |
| Limits | Input files up to 4 GB are read in pieces; the converted file is built in memory, so outputs above about 2 GB may fail. Needs a browser with WebCodecs (current Chrome, Edge, Safari 17+ or Firefox 130+). Other browsers are told so before any work starts. |
| Engine | Mediabunny (WebCodecs): streams are copied when compatible, otherwise re-encoded; MP3 via a WebAssembly encoder |
Limitations
- Only the main video and audio tracks are kept; subtitles and extra audio languages are not.
- Sound in a codec this browser cannot decode is left out.
- The MP4 is built in memory, so outputs above about 2 GB may fail.
- Needs a browser with WebCodecs: current Chrome or Edge, Safari 17 or later, or Firefox 130 or later. Other browsers are told so before any work starts.
Questions
Does converting MKV to MP4 lose quality?
Not when the MKV holds H.264 or H.265 video: the video is copied, not re-encoded, and the file list says so. VP9, AV1 and other video is re-encoded, which changes the picture slightly.
What happens to subtitles and extra audio tracks?
Only the main video track and the main audio track are written to the MP4. Subtitle tracks and additional audio languages are left out.
Why is the sound missing from my MP4?
MP4 keeps AAC and MP3 sound as it is. Other sound, such as Opus, FLAC or AC-3, is re-encoded to AAC when this browser can decode it; if it cannot, the audio is left out and the file list explains why.
Privacy
Runs on your device. Files and text are processed in this browser tab and are not uploaded.
This page opens the Video format converter ready for this task. See the privacy policy for how toolsdocks handles data.