MKV to MP4 Converter
Convert Matroska MKV files to MP4 so TVs, phones, and editors accept them. Most files remux in seconds with no quality loss.
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MKV Is a Box, Not a Codec
Matroska (.mkv) is a container format, and an unusually capable one. It can hold any number of video tracks, audio tracks in a dozen languages, soft subtitles, chapter markers, cover art, and attached fonts — all in one file. That flexibility is exactly why it became the standard for archived films, anime releases, and Blu-ray rips.
It is also why so little consumer hardware supports it. Smart TVs, game consoles, iPhones, iPads, PowerPoint, Premiere Pro, and almost every upload form expect MP4. The video insidethe MKV is very often already H.264 or HEVC — the same codec an MP4 would use. Only the box around it is wrong.
When that is the case, this tool copies the video and audio across without touching a single frame and rebuilds the container as MP4. A two-hour film can finish in under a minute, and the picture is identical to the source.
What MP4 Cannot Carry
MKV holds things MP4 has no place for, and this is where conversions usually go wrong on other tools:
- Subtitle tracks — MKV usually carries SRT or ASS/SSA subtitles. MP4 uses a different subtitle format entirely, and copying them across produces a file that either fails to build or shows nothing. This tool drops them rather than shipping a broken file.
- Multiple audio languages — MP4 technically supports several audio tracks, but player support is patchy. Only the first audio track is kept.
- Chapters and attachments — chapter markers and embedded fonts are Matroska features and do not survive.
- DTS and FLAC audio — common in Blu-ray rips, not valid in MP4. These get re-encoded to AAC at 192 kbps.
- VP9 or AV1 video — AV1 in MP4 is fine and gets copied; VP9 is re-encoded to H.264 for compatibility.
If subtitles matter to you, keep the original MKV and play it in VLC or MPV, both of which handle Matroska natively. Converting is for getting a file into hardware and software that refuses MKV outright.
How to Use
- Drag in a .mkv file. It stays on your machine — nothing is uploaded.
- Click Convert to MP4. The tool reads the stream list first and picks the fastest safe route.
- “Copied streams” means a lossless remux — expect seconds, not minutes.
- A re-encode message means the codec was incompatible, and it will take roughly 1–3 minutes per minute of 1080p footage.
- Preview and download.
Technical notes
- Fast path: H.264, HEVC, AV1, or MPEG-4 video with AAC, MP3, or AC-3 audio is copied stream-for-stream
- Slow path: anything else becomes H.264 (CRF 23) with AAC audio at 192 kbps
- Streams kept: first video track, first audio track. Subtitles, chapters, attachments, and extra languages are dropped
- faststart: the index is written to the front so the file streams properly from a web server
- Timestamps: MKV uses variable frame rate more often than MP4 does; the original timestamps are preserved, so audio sync is maintained
FAQ
Will the video quality drop?
Not in the common case. If the MKV already contains H.264 or HEVC, the frames are copied bit-for-bit into the new container. The tool tells you after conversion whether it copied or re-encoded.
Where did my subtitles go?
They were dropped on purpose. MKV subtitles are usually SRT or ASS, which MP4 cannot store in the same form; copying them blindly produces a file that fails to build or plays with no subtitles at all. To keep subtitles you would need to burn them into the picture, which requires a full re-encode.
The file had English and Japanese audio. Which one did I get?
The first audio track in the file, which is normally the default one the player would have picked. Selecting a specific language track requires a tool that lets you choose streams manually, such as MKVToolNix on the desktop.
Is the file size the same?
Almost. A remux only changes container overhead, so expect a difference of a percent or two — sometimes slightly smaller, because dropped subtitle and attachment tracks go away.
Why does my 4 GB movie fail?
The limit here is browser memory: the whole file has to fit inside the tab. For feature-length films, desktop FFmpeg is the right tool — ffmpeg -i input.mkv -map 0:v:0 -map 0:a:0 -c copy -movflags faststart output.mp4 is the exact command this page runs.
Should I convert at all, or just use a different player?
If you are watching on a computer, install VLC or MPV and keep the MKV — you lose nothing and keep the subtitles. Convert only when the destination genuinely refuses MKV: TVs, consoles, phones, editors, and upload forms.
Can I keep more than one audio track?
Not with this tool — only the first is carried across, because MP4 player support for multiple audio tracks is inconsistent. MKVToolNix on the desktop gives full control over stream selection.
Does the video resolution change?
No. On the fast path nothing about the picture changes at all, and even on the re-encode path only odd pixel dimensions are rounded down to even.
⚠️ Reference Only
Output is generated based on your input and is provided for reference. Results may vary depending on your specific use case, edge cases, or environment-specific behavior. We do not guarantee accuracy of conversions, validations, or computed values.
Always verify critical outputs against official documentation or production environments. We are not responsible for any decisions or losses based on these tool results.