Convert MP4 to MKV Online
Convert MP4 video to MKV instantly in your browser. Batch convert, preserve resolution, and download - zero uploads, 100% private.
Video encoding is heavier than audio or image processing - larger or longer files take longer, and up to 5 files can be queued at once to keep things responsive.
Drag & drop files, or browse
Up to 5 video files at once
How to convert MP4 to MKV
Upload your files
Drag & drop or browse up to 5 MP4 files at once.
Browser converts locally
FFmpeg (compiled to WebAssembly) converts to MKV in your browser - nothing is uploaded anywhere.
Download results
Save files individually or download everything as a ZIP bundle.
Why use this converter
100% private
Your MP4 files convert entirely in your browser - nothing is ever uploaded to a server.
Preserves resolution
Your video's original resolution and aspect ratio are kept - this tool changes format, not size (use Compress for that).
Fast encoding preset
Uses a speed-optimized encoding preset so conversion doesn't take longer than necessary in your browser.
No file size limits
Since nothing uploads to a server, there's no artificial cap on how large a file you can convert - just your device's own memory.
Frequently asked questions
4 questionsYes - conversion happens locally in your browser using FFmpeg compiled to WebAssembly, so there's no per-file cost, watermark, or account required.