Is this MP4 to MKV converter really free?

Yes. Up to 5 files at a time, no signup, no catch. The free tier adds a small watermark to image output — Pro ($9.99/mo or $49/yr) removes it, raises the file size limit to 500 MB, and unlocks unlimited batch conversion.

Are my files uploaded to a server?

No — and you can verify it yourself. Open DevTools → Network tab, then convert a file. You'll see zero upload requests. Everything runs right in your browser. We never see your files.

How long does conversion take?

Usually 1–3 seconds for a typical file. The very first conversion on a fresh page load may take 5–20 seconds while the converter engine loads — after that it's instant. Your CPU does all the work locally.

What is the file size limit?

Free: up to 10 MB per file, 5 files per batch. Pro: up to 500 MB per file, unlimited batch. If you're working with large videos or RAW photos, Pro is built for that.

Can I batch convert multiple MP4 files at once?

Yes — drop multiple files at once (or Ctrl/Cmd+click to select them) and they all convert in parallel. Free accounts handle up to 5 files per batch; Pro has no limit.

How large can my video files be?

Free accounts support files up to 10 MB — enough for short clips and GIFs. Pro raises that to 500 MB, which covers most 1080p videos. For files over 1 GB, a native app like HandBrake will be faster.

Will the video lose quality during conversion?

When only the container changes (e.g., MKV → MP4 where both use H.264), there's zero quality loss — it's a lossless rewrap. When the codec changes, we encode at CRF 23, which is near-transparent for most content.

Does converting MP4 to MKV re-encode the video?

No — it's a container swap. The H.264 video stream is moved directly into an MKV container without re-encoding. The process is fast and lossless.

Why would I want MKV over MP4?

MKV supports multiple audio tracks, subtitle tracks, and chapters in a single file. It's the preferred container for media players like VLC, Kodi, and Plex that support those features.

How private is this converter?

Completely private — by design, not policy. There is no upload endpoint. Files are processed right inside your browser tab and disappear the moment you close it. We collect only anonymous page-view counts; your file content is never seen or stored.

MP4 to MKV — Free, Fast, No Upload

How to convert MP4 to MKV online

1
Drop your MP4 file
Drag and drop your MPEG-4 Part 14 file onto the converter, or click to browse your files. You can select up to 5 at once. Nothing leaves your device — conversion happens right here in the browser.
2
Hit Convert — it happens locally
Click Convert and watch it go. There's no upload, no server queue, no waiting. The converter runs MPEG-4 Part 14 → Matroska Video entirely in your browser tab. Most files finish in 1–3 seconds.
3
Download your MKV
Your Matroska Video file is ready. Click Download, or grab a ZIP if you converted a batch. Close the tab and everything disappears — no copies kept anywhere.

MP4 vs MKV: format overview

MP4

MPEG-4 Part 14

Moving Picture Experts Group · 2001

Compression: lossy
Transparency: No

✓ Universal compatibility across all platforms
✓ Excellent compression with H.264/H.265
✗ H.264 has royalty implications

MKV

Matroska Video

Matroska.org · 2002

Compression: lossy
Transparency: No

✓ Supports virtually any codec combination
✓ Multiple audio tracks and subtitles per file

MP4 magic bytes: 00 00 00 xx 66 74 79 70

MKV magic bytes: 1A 45 DF A3

Why convert MP4 to MKV?

If you've ever tried to open a MP4 file and hit a wall — the app won't accept it, the website rejects it, or the preview just shows a broken icon — you already know why this conversion matters.

MPEG-4 Part 14 is great for what it was designed for, but it has real-world limitations: h.264 has royalty implications and not ideal for video editing (better to edit in prores/dnxhd). The moment you step outside that original context, it gets frustrating fast.

Matroska Video is the safer choice for Movie archiving, Anime downloads, Multi-language video distribution. Its main advantages — supports virtually any codec combination and multiple audio tracks and subtitles per file — mean it just works wherever you need it.

A few common reasons people end up here: - Their target app, site, or device doesn't accept MP4 - They need a smaller file for email or upload (MKV often compresses better) - They need Matroska Video's specific capability: supports virtually any codec combination - Compatibility with older software that pre-dates MPEG-4 Part 14

The conversion is one-way: you get a MKV that works everywhere Matroska Video is expected. The original MP4 file is not touched.

Quality & file size: MP4 to MKV

Typical file sizes: MP4 100–300 MB → MKV 200–800 MB.

Both MP4 and MKV use lossy compression. We transcode at high quality settings (equivalent to MKV's recommended web quality) to minimize generational loss.

Color depth: MP4 supports standard color, MKV supports standard color.

Transparency: MP4 does not support transparency. MKV does not support transparency — transparent areas become solid white.

Frequently asked questions

Privacy: how FormatDrop handles your files

Your MP4files are converted 100% inside your browser. They are never uploaded to our servers, never stored, and never seen by anyone other than you. This isn't a privacy policy claim — it's an architectural guarantee: our server has no endpoint that receives file bytes.