How to Convert MP4 to MKV Online Free — No Upload Needed

What Is MKV and Why Convert from MP4?

MKV (Matroska) is an open-standard container format that supports virtually any video codec,

multiple audio tracks, subtitle streams, and chapter markers — making it the preferred archival format.

MP4 is great for sharing and streaming, but MKV is better for local storage and playback flexibility.

MKV also has no patent restrictions, making it the format of choice for archiving high-quality video.

How to Convert MP4 to MKV Online (No Upload)

Our free FFmpeg converter runs entirely in your browser using WebAssembly.

Your file never leaves your device — conversion is 100% local.

Steps:

1. Drag and drop your MP4 file onto the converter

2. Select MKV as the output format

3. Click Convert

4. Download your MKV file instantly

No signup. No file size limit. No quality loss.

Why Use FFmpeg for MP4 to MKV?

FFmpeg stream-copies the video and audio data — no re-encoding required.

This means:

• Conversion is near-instant — no encoding overhead
• Zero quality loss — the data is identical to the source
• No additional software — runs in your browser via WebAssembly

The command equivalent is: ffmpeg -i input.mp4 -c copy output.mkv

MP4 to MKV: What Changes?

Only the container changes — not the video or audio data. The H.264 or H.265 video stream,

and the AAC audio stream, are moved into the MKV container unchanged.

Does MKV Reduce Quality?

No. Stream copying preserves 100% of the original quality. MKV is a container, not a codec.

If you want to compress the video, use custom FFmpeg args like -c:v libx264 -crf 23.

Try It Now

Use our free MP4 to MKV converter — no signup, no upload, unlimited conversions.