What is the mkv to mp4?
MKV to MP4 turns a Matroska file into a widely playable MP4 using FFmpeg in the browser. Because most MKVs already hold H.264 and AAC, it usually does a fast, lossless remux, copying streams into an MP4 shell with no quality loss, plus a re-encode fallback for odd codecs. Free, nothing uploaded.
This MKV-to-MP4 converter runs a full FFmpeg build compiled to WebAssembly right in your browser and turns a Matroska (.mkv) file into an MP4 that actually plays where you need it. MKV is a wonderfully flexible container (it's what rippers, encoders and archivists reach for because it can hold almost anything) but that flexibility is exactly why it trips up so much of the real world: iPhones and many Android players, smart TVs, QuickTime, a lot of video editors, most messengers, and a plain HTML `<video>` tag either refuse it outright or play the video with no sound. MP4 is the opposite: it's the universal, boring, works-everywhere container. Here's The upside the upload sites gloss over: the overwhelming majority of MKVs already carry H.264 video and AAC audio inside them, and MP4 is happy to hold exactly those streams. So most conversions are a REMUX, the tool copies the existing video and audio streams straight into an MP4 shell without decoding or re-encoding a single frame. That's lossless (the picture and sound are bit-for-bit identical), it's fast (a full movie can finish in seconds), and it produces a file roughly the same size as the source. If the inner codecs aren't MP4-friendly. Say the audio is FLAC, Vorbis or an unusual track, or the video is a format MP4 can't carry. You can switch to a full re-encode to H.264/AAC for maximum compatibility, at the cost of time and a small quality hit. Everything is client-side, so there's no upload wait and no privacy tradeoff: ripped discs, downloaded recordings, camera dumps and unreleased footage never leave your machine, and there's no server to store, log or leak them. Be honest about the edges: WebAssembly FFmpeg is single-threaded and memory-bound, so a re-encode of a long or high-resolution clip takes real time, and browsers can't handle every exotic MKV codec (some Blu-ray audio formats and certain 10-bit HEVC streams may not survive). But for the common case, an MKV that just won't play, drop it in and get a clean, universal MP4 back in seconds, entirely in the browser.
- Difficulty:
- Medium
- Typical time:
- ~1–2m
- Processing:
- 100% browser processing
- Converts:
- MKV → MP4
Last updated
How to use the mkv to mp4
- 1
Drop your MKV
Drag a.mkv file onto the workspace, or click to browse. It's probed locally for duration and dimensions: nothing is uploaded.
- 2
Pick a mode
Leave it on the fast, lossless remux (best for the usual H.264/AAC MKV), or switch to full re-encode if the file has an unusual codec or won't remux cleanly.
- 3
Convert & preview
Click Convert to MP4. FFmpeg loads once (a one-time download), a progress bar tracks the work, and the finished MP4 plays right in the page.
- 4
Download or restart
Save the MP4, or reset and try the other mode if the remux couldn't carry a track and you'd rather re-encode for full compatibility.
What MKV to MP4 includes
Fast, lossless remux
Most MKVs already hold H.264 + AAC, so the tool copies those streams straight into an MP4 shell. No re-encode, no quality loss, and a full movie can finish in seconds.
Plays everywhere MKV won't
MP4 is the universal container: iPhones, Android, smart TVs, QuickTime, editors, messengers and a plain <video> tag all accept it, where MKV so often gets rejected or plays silent.
Re-encode fallback for odd codecs
If the inner audio or video isn't MP4-friendly (FLAC, Vorbis, an exotic track), switch to a full H.264/AAC re-encode for maximum compatibility, at the cost of time.
Preview before you download
The finished MP4 plays right in the tool with its exact file size, so you can confirm the picture and audio survived before you save or share it.
Same size, same quality
A remux keeps the original streams bit-for-bit, so the MP4 is roughly the same size as the MKV and looks and sounds identical: you're only changing the wrapper.
100% in your browser
FFmpeg runs as WebAssembly on your device. Your MKV is never uploaded, stored or logged, safe for ripped discs, private recordings and unreleased footage.
Why use our mkv to mp4
Get a file that just plays
An MKV that iOS, your TV or your editor refuses becomes a plain MP4 that opens everywhere, usually in seconds, because most files only need a container swap, not a re-encode.
Keep every pixel of quality
Because the common path is a lossless remux, the video and audio are copied untouched. You get MP4 compatibility with zero generational quality loss, something upload converters that always re-encode can't promise.
Keep your footage private
Nothing leaves your device. A ripped disc, a downloaded recording or an internal capture is converted on-device, so there's no server that ever sees your file.
No install, no watermark, no sign-up
Get a real MP4 without desktop software like HandBrake or VLC, without a login, and without a logo stamped on your video: just a browser tab you can close when you're done.
Built for the way you work
From quick one-off fixes to daily workflows, see how people put this tool to use.
- Movie & TV ripper
Play a ripped MKV on an iPhone or TV
Discs and downloads land as MKV, which iOS and many smart TVs won't touch. Remux to MP4 locally in seconds, lossless, so it plays on the couch or the phone without a media-server workaround.
- Video editor
Import footage your NLE rejects
Premiere, Final Cut and many editors don't like MKV. Convert to MP4 first, usually a fast remux that preserves the original quality, so the clip drops straight onto the timeline.
- Anyone sharing a clip
Send a video that opens for everyone
Messengers and phones often choke on MKV. Hand people an MP4 instead and it previews and plays inline. No 'unsupported format' and no missing audio.
- Web developer
A <video> source that works
Browsers won't stream MKV in a <video> tag. Convert to MP4 (H.264/AAC) so a hero clip or embedded demo plays natively, encoded on-device, so a pre-launch asset stays private.
Supported formats
Accepts MKV, and produces MP4, all processed locally in your browser.
- MKV
- MP4
Frequently asked questions
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Common problems, solved
Hit a snag? Here are quick fixes for the issues people run into most.
The MP4 plays but has no sound.
The remux copied an audio codec MP4 can carry, but that MKV's audio was likely FLAC, Vorbis or another non-MP4 track that couldn't be copied as-is. Reset and switch to the full re-encode mode. It transcodes audio to AAC, which MP4 always supports.
The remux failed or the video won't play.
The MKV's video codec probably can't live in an MP4 container (some 10-bit HEVC or exotic streams). Switch to re-encode mode to transcode the video to H.264, which every MP4 player understands. It's slower but far more compatible.
The re-encode is slow.
Re-encoding runs H.264 in single-threaded WebAssembly, which is much slower than a native tool. Long or high-resolution files are the worst case. If your MKV is a standard H.264/AAC file, use the remux mode instead: it copies streams and finishes in seconds.
Nothing happens on the first click, or there's a pause before progress.
The first conversion downloads the FFmpeg WebAssembly core (~31 MB) once, then caches it. Give it a moment on the first run. Later conversions in the same session start immediately.
Get the most out of it
Try the fast remux first. Most MKVs are already H.264/AAC, so it converts losslessly in seconds. Only fall back to re-encode if a track won't carry over.
A remux keeps the original quality and size. A re-encode is your compatibility safety net when the remux plays silent or fails.
If you only need a clip, trim the MKV first (the Video Trimmer): a shorter file re-encodes far faster if you do need that mode.
For very large discs, close other heavy tabs before converting: WebAssembly FFmpeg is memory-bound and a full movie is a lot to hold at once.
Keep the original MKV until you've confirmed the MP4 plays with sound. Then you can safely delete the source.
What's new
Recent updates and improvements to the mkv to mp4.
Initial release, browser-side MKV-to-MP4 conversion via WebAssembly FFmpeg, with a fast lossless remux mode (stream copy) plus a full H.264/AAC re-encode fallback, a live progress bar, in-page preview and download. Nothing is uploaded.
Made the lossless remux the default and added clearer guidance for the silent-audio case (FLAC/Vorbis tracks) that needs the re-encode fallback.
Sharpened honest limits around exotic MKV codecs (some Blu-ray audio and 10-bit HEVC) and improved memory handling so full-length movies remux more reliably.
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Your privacy is built in
Your MKV is converted to MP4 entirely in your browser using FFmpeg compiled to WebAssembly. It is never uploaded to any server. Nothing is stored, logged or transmitted, so you can safely convert ripped discs, private recordings and unreleased footage. The FFmpeg core is fetched once from this site (same-origin) and cached. Your media stays on your device. Close the tab and every trace is gone.
- Runs in your browser
- No uploads
- Nothing stored
Ready to try the mkv to mp4?
Free, private and instant. MKV to MP4 runs right in your browser.