MKV to MP4

How to use MKV to MP4

1. Choose one or more .mkv files.
2. Press Convert to MP4; the encoder settings are fixed for broad playback support.
3. Leave the tab open while each file is encoded; the percentage shows progress.
4. Download the MP4, or all results together as a ZIP.

MKV and MP4 are containers, not codecs

MKV is a flexible open container that can hold almost any codec, several audio languages, chapters and many subtitle tracks, which is why it is popular for downloads and rips and loved by VLC, Kodi and Plex. MP4 is stricter, but it is the format that iPhones, Android galleries, TVs and upload sites expect.

This tool does not merely rewrap the streams; it re-encodes video with libx264 at CRF 23 in 8-bit yuv420p and audio as 128 kbps AAC. That guarantees a playable result even when the MKV holds HEVC, VP9, AC-3 or DTS, at the cost of encoding time and a small generation loss.

Limitations

• Only one video and one audio track are kept. FFmpeg picks the audio track it ranks highest, usually the one with most channels, which may not be the language you want.
• MKVs with image-based subtitles (PGS from Blu-ray rips or VobSub) may fail, because MP4 can only take text subtitles. Text subtitles lose their styling.
• Full-length films are heavy for browser memory; above roughly 500 MB the conversion may stop.

Frequently asked questions

Why does my TV or phone not play MKV?

Many built-in players support the codecs but not the Matroska container, or lack decoders for the audio, such as DTS. MP4 with H.264 and AAC avoids both problems.

Is the conversion lossless?

No. Video and audio are re-encoded. CRF 23 is close to the source visually, but it is not a bit-for-bit copy.

Why is my 5.1 audio now stereo?

It need not be; AAC can carry 5.1. If your source had several tracks, the one FFmpeg chose may simply have been the stereo track.

Does the MKV get uploaded?

No. FFmpeg runs as WebAssembly inside this page, so the file is converted locally.