How to Convert MKV to MP4 Online
Convert MKV video files to MP4 format in your browser. No upload, no software — fast and private conversion.
MKV (Matroska) is a versatile video container that supports multiple audio and subtitle tracks. However, many devices and platforms — particularly iPhones, Smart TVs, and social media — require MP4 format.
ConvertCraft's Video Converter uses browser-based FFmpeg (WebAssembly) to remux or transcode MKV to MP4. If both files use H.264 video, the conversion is a near-instant remux with zero quality loss.
To convert: open the Video Converter, drop your MKV file, select MP4 as the output format, and click Convert. For compatible streams, the tool detects that remuxing is possible and skips slow transcoding.
If the MKV contains codecs not supported by MP4 (like VP9 video or Opus audio), the tool will transcode to H.264 + AAC — the most universally compatible codec combination.
The converter preserves the first audio track and first subtitle track by default. For MKV files with multiple audio languages, you can select which track to include in the MP4 output.
Frequently Asked Questions
Does MKV to MP4 conversion lose quality?
If both use H.264 video, the conversion is a lossless remux — just repackaging the same data. If transcoding is needed, there is a minor quality reduction.
Why is the conversion sometimes instant and sometimes slow?
Instant conversion means the streams are compatible and only the container is changed (remux). Slow conversion means the video or audio codec needs to be transcoded.
Can I keep subtitles when converting to MP4?
MP4 supports embedded subtitles in SRT/MOV-text format. The converter preserves the first subtitle track. For complex subtitle formats (PGS, ASS), they may be converted or stripped.