offlinewebtools.com — free, watermark-free browser tools that stay on your device with nothing uploading to our servers

MP4 to MKV Converter

Convert MP4 videos to MKV format, supporting multiple audio tracks, subtitles, and chapters in a flexible container.

Free to use, no watermarks, runs in your browser—nothing uploads to our servers

Source file

Files are processed locally in your browser using WebAssembly.

Quality (CRF)

Lower = better quality (0-51, default: 23)

Report a bug

If this tool misbehaves, share a quick summary so we can investigate. We include the tool URL automatically—no need to copy and paste.