MKV vs MP4
| Property | MKV | MP4 |
|---|---|---|
| Full name | Matroska Video | MPEG-4 Part 14 |
| File extensions | .mkv | .mp4, .m4v |
| Created by | Matroska open-source project | MPEG (ISO/IEC 14496-14) |
| Introduced | 2002 | 2003 |
| Compression | Depends on the codec; usually lossy | Depends on the codec inside; usually lossy |
| Codecs inside | Almost any: H.264, HEVC, VP9, AV1 video; AAC, Opus, AC-3, DTS audio; many subtitle tracks | Usually H.264 or H.265 video with AAC audio |
| Opens on | VLC and desktop players; not iPhone, Safari, many TVs, editors or social networks | Every phone, computer, TV, browser, editor and social network |
| Best for | Films with several audio and subtitle tracks; crash-safe recordings | Sharing, uploading and playing video anywhere |
Why convert MKV to MP4?
Matroska (MKV) is a flexible container that can carry almost any codec plus several audio and subtitle tracks. That flexibility is why many recorders and media servers use it, and why many devices refuse it: iPhones, Safari, a lot of smart TVs, Premiere Pro's older versions and most social networks expect MP4.
Because MKV and MP4 can both carry H.264 video and AAC audio, converting is usually a remux: the same compressed streams are copied into a new container. That is fast and lossless. If the MKV contains something MP4 players handle poorly, such as VP9 video or Opus, the converter re-encodes it to H.264 and AAC.
Two limits to know. The MP4 keeps the main video and audio track only; extra language tracks and subtitles in the MKV are not copied. And surround formats such as DTS or Dolby Digital may not be decodable in a browser, in which case the tool tells you the audio was left out rather than producing a broken file. To make the MP4 smaller afterwards, use the Video Compressor.