Convert MP4 to MKV Online — No Upload, No Watermark
MKV is a flexible open container that holds multiple audio tracks, subtitle tracks, and chapter markers in one file — useful for archival or multilingual releases.
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Tamaño máximo: ~2 GB (según memoria)
Why convert MP4 to MKV here?
- MKV stores subtitles, metadata, and multiple audio tracks more cleanly than MP4.
- No re-encoding required — the H.264 + AAC streams are repackaged into MKV in seconds.
- Lossless remux: pixel-identical and sample-identical output.
FAQ
Is this MP4 to MKV converter really free and without upload?
Yes. The tool runs entirely in your browser using FFmpeg compiled to WebAssembly. Your MP4 file never leaves your device — open the DevTools Network tab to verify zero uploads. No signup, no watermark, no size cap beyond browser memory (~2 GB).
Will converting MP4 to MKV reduce quality?
The converter re-encodes to MKV with CRF 23 (visually lossless for most footage). If you need stream-copy instead (no re-encoding), use the Converter tool directly and toggle the codec-copy option.
How long does MP4 to MKV conversion take?
On an M2 MacBook, a 1-minute 1080p clip converts in about 8 seconds. 4K clips scale roughly linearly. Old machines are slower — processing uses your CPU and GPU, not our servers.
Can I batch-convert multiple MP4 files?
Not yet — the current flow converts one file at a time. Queue multiple tabs if you need parallel conversion.