Convert MP4 to MKV — Free & Private
Convert MP4 to MKV online for free. MP4 is the most universally compatible video format; MKV is a flexible container format that supports multiple streams. All processing happens locally in your browser — your files never leave your device.
How to convert MP4 to MKV
- 1
Select your MP4 file
Click or drag your MP4 file onto the converter above.
- 2
Convert to MKV
The output format is pre-set to MKV. Click the convert button to process your file.
- 3
Save instantly
Your converted MKV file is ready — save it to your device, no email required.
MP4 to MKV — FAQ
Is the MP4 to MKV converter really free?
Yes, completely free. No hidden fees, no watermarks, no file size limits. LocalConvert is open source and free forever.
Are my MP4 files safe?
Absolutely. Your files never leave your browser. All MP4 to MKV conversion happens using WebAssembly running locally on your device — no uploads, ever.
How long does MP4 to MKV conversion take?
Most conversions finish in seconds. Larger files may take a little longer depending on your device's speed and memory.
What's the difference between MP4 and MKV?
MP4 is the most universally compatible video format. MKV is a flexible container format that supports multiple streams.