MKV to MP4 Converter

MKV to MP4, in seconds. Nothing ever uploads.

Drop an MKV below — remuxed to MP4 entirely on your device. H.264/HEVC files copy over with zero quality loss.

  • Zero uploads — verifiable
  • Unlimited free use
  • Batch up to 5 files
  • Remux in seconds, no re-encode

Convert MKV to MP4

Add your MKV files

Drag & drop MKV files here

or browse your files · up to 5 files, 200 MB each

Converter loads only when you convert your first file — the page stays light until then.

    No files yet. Everything stays on this device. Downloads start instantly.
    Conversion settings
    Conversion mode

    Automatic: H.264/HEVC files remux in seconds with zero quality loss; anything else is transcoded to H.264 + AAC at your chosen quality below.

    Transcode quality (only used when re-encoding is needed)

    Remuxed files ignore this setting entirely — a stream copy has no quality setting to choose.

    What always happens

    Subtitles are dropped (MP4 players handle them inconsistently). Only the first video track and first audio track are kept. Audio that cannot be copied (DTS, FLAC, Opus) is converted to AAC at 128 kbps. Output is H.264 + AAC in an MP4 with fast-start, so it plays before fully downloading.

    Privacy you can verify, not just trust

    Most online MKV to MP4 converters upload your file to their servers first — and some keep a download link live for 30 days. This one can't: the converter runs entirely in your browser. Your videos are never sent anywhere — the only requests to other sites are the site's own analytics, which count page views — and it uploads nothing, ever. The only file fetched after load for the conversion itself is the encoder (~31 MB, from this same site, once, on your first convert) — it carries no video data. Don't take our word for it:

    External requests during processing: 0 (zero — as it should be)
    1. Press F12 to open developer tools, then the Network tab.
    2. Convert any MKV above. Watch: apart from the site's analytics, the only request is the encoder file from this site — no uploads, and no video data ever leaves your device.
    3. Extra credit: disconnect your internet after this page loads — conversion still works.

    How to convert MKV to MP4 without uploading it

    MKV is a flexible container — it can hold almost any video and audio codec — but that flexibility is exactly why so many devices refuse to play it. Phones, smart TVs, game consoles and browsers all understand MP4, and most of them only really trust one combination: H.264 video with AAC audio. Converting MKV to MP4 is usually just a matter of putting the streams you already have into the wrapper every device understands.

    This tool does exactly that, on your own device. When you drop an MKV here, your browser:

    1. Loads a real video converter (ffmpeg, compiled to WebAssembly) — but only when you convert your first file, so the page itself stays light.
    2. Reads the file's streams — which video codec, which audio codec, whether there are subtitles — and decides the fastest honest path for that file.
    3. Remuxes when it can: if the video is H.264 or HEVC and the audio is AAC or MP3, both streams are copied bit-for-bit into a new MP4. No decoding, no re-encoding, no quality loss — a file that would take minutes to re-encode finishes in seconds.
    4. Transcodes only what must change: VP9 or AV1 video is re-encoded to H.264, and DTS, FLAC or Opus audio to AAC (128 kbps). Streams that are already compatible are still copied, never re-encoded.
    5. Hands you an MP4 as a download, with fast-start enabled so it begins playing before it has fully downloaded. Your original MKV is never modified.

    Why is MKV to MP4 usually instant?

    Because in most cases nothing is actually being converted. The video and audio inside a typical MKV are already H.264 and AAC — the same streams an MP4 holds. Re-encoding them would be pure waste: slower, larger or lower quality, for no benefit. Remuxing just re-wraps them, which is why this tool checks the codecs first and tells you which path each file took, instead of re-encoding everything the way most online converters do.

    When transcoding is unavoidable

    Some MKV files hold codecs that have no legal home in a broadly playable MP4. VP9 and AV1 video (common in files downloaded from the web) and DTS, FLAC or Opus audio (common in Blu-ray rips) must be re-encoded. That takes roughly real time or slower in a browser tab, and it loses a little quality — the tool uses CRF 20 by default, where the loss is hard to spot, and says so plainly on the file card instead of pretending the conversion was lossless.

    Honest limitations

    Subtitles are dropped

    MP4 players handle subtitle tracks inconsistently, so this tool leaves them out rather than burning them into the picture. Keep the original MKV if you need the subtitles.

    Only the first audio track

    If your MKV has several audio tracks — multiple languages, a commentary track — only the first is kept. The rest are dropped, and the card says so.

    HEVC plays on most, not all, devices

    HEVC (H.265) video is copied as-is, and it plays on most modern phones, TVs and browsers. Very old devices often lack HEVC decoding — if yours struggles, re-encode to H.264 with a desktop tool.

    Transcoding is slow and slightly lossy

    VP9/AV1 video and DTS/FLAC/Opus audio must be re-encoded. Expect roughly real time or slower in a browser tab, and a small quality loss — the card tells you when this happened.

    200 MB per file, 5 files per batch

    The converter holds the whole file in tab memory, so multi-GB files — a full movie rip — can crash the tab. Large files belong in a desktop converter like HandBrake.

    Remuxing is lossless; transcoding is not

    A remuxed MP4 is bit-for-bit identical in quality to the MKV. A transcoded one is not — the tool shows which path each file took, so you always know what you got.

    Frequently asked questions

    How do I convert MKV to MP4 without uploading it anywhere?

    Use a tool that converts files locally in your browser. This converter loads ffmpeg (compiled to WebAssembly) into your device, reads your MKV's video and audio streams, and either copies them straight into an MP4 container (remuxing) or re-encodes them to H.264 + AAC — all with JavaScript running on your machine. No file data is sent to any server; verify it in your browser's Network tab.

    What is remuxing, and why is it faster than converting?

    Remuxing changes only the container, not the video itself. An MKV and an MP4 are both wrappers around the same kind of video and audio streams — if your MKV already holds H.264 or HEVC video with AAC or MP3 audio, those streams are already legal MP4 contents, so the tool just copies them into a new MP4 file. No decoding, no re-encoding: a 1 GB file remuxes in seconds on a normal computer, while re-encoding the same file would take minutes and lose a little quality. This tool remuxes whenever it can and only re-encodes the streams that truly need it.

    Will converting MKV to MP4 lose quality?

    Not when the file is remuxed. Remuxing copies the video and audio bit-for-bit, so the MP4 is identical in quality to the MKV — the same pixels, the same sound, just a different wrapper. Most MKV files are H.264, so most files take this path. If your file holds VP9 or AV1 video (or DTS/FLAC/Opus audio), those streams cannot live in a broadly playable MP4 and must be re-encoded to H.264 + AAC, which does lose a little quality — the tool tells you which path each file took and uses CRF 20 by default, a setting where the loss is hard to spot.

    What happens to subtitles and extra audio tracks?

    Subtitles are not carried over. MP4 players handle subtitle tracks inconsistently, so this tool leaves them out rather than burning them into the picture or producing a file some players mishandle — each file card says so plainly when a subtitle track is dropped. Only the first video track and the first audio track are kept; if your MKV has several audio tracks (for example, multiple languages), the rest are dropped. Keep the original MKV if you need the subtitles or the other languages.

    Will the MP4 play on my phone, TV, or older device?

    An MP4 with H.264 video and AAC audio plays on practically everything — phones, TVs, browsers, game consoles, and old laptops. That is the whole point of converting: MKV is flexible but poorly supported, while H.264 MP4 is the one format every device understands. One exception: if your MKV holds HEVC (H.265) video, the tool copies it as-is, and HEVC in MP4 plays on most modern devices but older ones may struggle — very old phones, TVs and laptops often lack HEVC hardware decoding. If an HEVC file will not play on your device, re-encode it to H.264 with a desktop tool (HandBrake is free) — this converter copies HEVC as-is and never re-encodes it.

    How big can the MKV file be?

    200 MB per file, up to 5 files per batch. The converter runs entirely in your browser tab and holds the whole file in memory, so a larger input can crash the tab — multi-GB files, like a full movie rip, exceed what a browser tab can practically hold and need a desktop converter (HandBrake or Shutter Encoder, both free). There is no duration limit for remuxed files, but transcoding a long file is slow — roughly real time or slower — so files over 30 minutes that need transcoding come with a warning.

    Does this MKV to MP4 converter upload my files?

    No. All conversion happens on your device with ffmpeg.wasm, downloaded from this site once (about 31 MB, in two parts) and then run locally. Your files are never sent to any server; the only network requests on this page are the site's own analytics (Google Analytics and a Cloudflare beacon), which load when the page opens and never see your files. You can verify it in your browser's DevTools Network tab — the page shows a live counter of requests during processing, which stays at zero while a file converts.