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MKV to MP4Free online MKV to MP4 converter
Convert MKV to MP4 in your browser
MKV to MP4 is a free, browser-based converter that repackages Matroska (.mkv) video into MP4 without uploading it anywhere. For MP4-compatible codecs — H.264, H.265/HEVC, AV1 — it copies the video bit-for-bit, and the audio too when it is AAC, MP3, AC-3 or E-AC-3, so a typical file converts in seconds with zero quality loss.
Drop up to 20 files of 1.5 GB each, convert them in one batch, and download the results — no signup, no watermark, and once the engine has loaded with your first file it keeps working offline.
- 100% free
- No upload
- No quality loss
- Batch up to 20
- Offline once the engine loads
Files are processed on your device with FFmpeg compiled to WebAssembly — nothing is uploaded, logged, or stored.
How to convert MKV to MP4
Three steps, all inside your browser — your videos never touch a server.
Add your MKV files
Drag and drop up to 20 Matroska (.mkv) files into the zone above, or click it to browse your device. Each file can be up to 1.5 GB. The first file you add downloads a one-time ~31 MB conversion engine that your browser then caches.
Let the converter pick the fastest path
The tool reads each file's codecs and chooses automatically: H.264, H.265/HEVC, and AV1 video is copied into the MP4 container bit-for-bit (a remux — done in seconds, zero quality loss), while VP8/VP9 video or Opus/Vorbis/DTS audio is re-encoded to H.264/AAC so the MP4 plays everywhere.
Preview and download your MP4s
Play any finished MP4 right on the page to check the result, then save files one by one or grab everything at once with Download all. Your videos were processed locally — nothing was uploaded to any server.
Technical specifications
| Input format | MKV (Matroska), up to 1.5 GB per file |
|---|---|
| Output format | MP4 — H.264/H.265/AV1 video, AAC/MP3/AC3 audio |
| Conversion method | Stream copy (remux) when codecs allow — zero quality loss; automatic re-encode to H.264/AAC otherwise |
| Batch limit | Up to 20 files per batch, converted one after another |
| Typical speed | Seconds per file when remuxing — no re-encoding involved |
| Subtitles | SRT/ASS converted to MP4 timed text; a file with bitmap (PGS/VobSub) subtitles loses all its subtitle tracks |
| Processing location | 100% in your browser via FFmpeg compiled to WebAssembly — no upload |
| Price | Free — no signup, no watermark, no daily limits |
| Works offline | In the open tab, once the ~31 MB engine has downloaded with your first file |
Frequently asked questions
How do I convert MKV to MP4 without losing quality?
Drop the MKV file here — if its video track is H.264, H.265/HEVC, or AV1, the tool remuxes it: the compressed video is copied into the MP4 container bit-for-bit, so it is never decoded or re-compressed and its quality is untouched. The audio is copied the same way when every track is AAC, MP3, AC-3 or E-AC-3; otherwise all audio tracks are converted to AAC at 192 kbps. That is also why most conversions finish in seconds instead of minutes.
Is this MKV to MP4 converter really free?
Yes — completely free, with no signup, no watermark, and no daily conversion limits. The site is supported by ads; the converter itself never asks for payment or an account.
Are my videos uploaded to a server?
No. The converter is FFmpeg compiled to WebAssembly and runs inside your browser tab, so your files never leave your device. That is also why there is no upload wait, and why the tool keeps working offline once the conversion engine has downloaded with your first file.
Why convert MKV to MP4 at all?
Because MP4 plays almost everywhere and MKV does not. iPhones and iPads, smart TVs, game consoles, PowerPoint, and editors like Premiere Pro or CapCut all accept MP4, while MKV support is patchy. The video data inside both containers can be identical — MKV and MP4 are just different wrappers around the same streams.
Does converting MKV to MP4 reduce video quality?
No — not in the common case. For H.264, H.265/HEVC, and AV1 video the tool copies the video stream without re-encoding, so the picture is bit-identical to the source. Audio stays bit-identical when every track is AAC, MP3, AC-3 or E-AC-3; if any track is DTS, TrueHD, FLAC, Opus or Vorbis, all audio tracks are converted to AAC at 192 kbps. Only video in a codec MP4 players don't take — VP8/VP9, rare inside MKV, or an older one like MPEG-2 or VC-1 — has to be re-encoded to H.264, which is slower and involves one generation of compression.
What is the maximum file size?
1.5 GB per file, up to 20 files per batch. The cap comes from memory: the finished MP4 is held in your browser tab until you remove it from the list or close the tab, so the cap keeps a conversion within what a tab can reliably hold. There is no limit on how many batches you run.
What happens to the subtitles in my MKV?
Text subtitles (SRT, ASS/SSA) are converted to MP4's native timed-text format and kept. Bitmap subtitle tracks — PGS from Blu-rays or VobSub from DVDs — cannot be stored in an MP4, so a file that has any of them loses all its subtitle tracks, the text ones too; its video and audio convert as usual.
Does it work on a phone?
Yes — Chrome or Firefox on Android and Safari on iOS all run the WebAssembly engine. Phones have less free memory than desktops, so very large files are more likely to fail there; a laptop is the safer choice for files approaching the 1.5 GB limit.
About this tool
MKV to MP4 exists for one job: making an MKV file play where MKV won't — on an iPhone, a smart TV, a PowerPoint slide, a video editor's timeline — by moving it into the MP4 container those players expect.
Under the hood it runs FFmpeg compiled to WebAssembly, loaded once (~31 MB) and cached by your browser. Each file is inspected first: when the video is H.264, H.265/HEVC, or AV1, the tool performs a remux — the encoded streams are copied into the new container untouched, which takes seconds and cannot degrade quality because nothing is re-compressed. Only codecs MP4 players don't accept, like VP8/VP9 video or Opus/DTS audio, are re-encoded — and when one audio track needs it, every audio track goes to AAC — and the tool tells you which path it took for every file.
Because the whole pipeline runs on your device, there is nothing to upload, no queue to wait in, and no copy of your video on anyone's server — disconnect from the internet once the engine has loaded with your first file and conversions keep working.
Worried about quality? The tool remuxes by default — learn more on the MKV to MP4 without losing quality page. On a Mac, where QuickTime and iMovie refuse MKV files entirely, there is a dedicated guide: convert MKV to MP4 on Mac — same converter, with the macOS specifics explained. And if you are weighing this tool against desktop apps, the blog compares the two approaches step by step: converting MKV to MP4 with HandBrake.
Your videos never leave your device
Every conversion runs locally through WebAssembly FFmpeg. We never receive, store, or even see a byte of your video — there is no upload endpoint to send it to. Close the tab and nothing about your files persists anywhere.