MP4 to MKV Converter
Repack into MKV, keeping every audio track and subtitle without re-encoding.
Up to 50 MB per file. Sign up free to convert files up to 100 MB.
| File name | Size | Convert to |
|---|
Checking files and selected output formats.
What to expect when converting MP4 to MKV
Measured on a 720p H.264 MP4: 6.81 MB in, 6.80 MB out (-0.1%), done in 0.11s, about 134x faster than real time, because no frame is re-encoded.
Quality: None. The video and audio streams are copied into the new container untouched, so the result is bit-for-bit the same picture and sound.
Best for: keeping multiple audio tracks and subtitle streams together in one file, Plex and Kodi libraries, archiving.
Avoid when: the file is going to an iPhone, iPad, Apple TV or a social platform, those want MP4.
Tip: MKV accepts every stream your MP4 holds, so a file with two audio tracks and subtitles arrives intact. The conversion adds nothing new, it cannot create a subtitle track that was not already in the source.
MP4 to MKV: a container swap, not a conversion
MP4 and MKV (Matroska) are both containers, wrappers around the video and audio streams inside. Moving an MP4 into MKV does not touch those streams: the H.264 video and AAC audio are copied across byte for byte, which is why a 720p file measured here finished in 0.11 seconds, roughly 134 times faster than playing it. Quality is identical because nothing is re-encoded. What changes is what the container will accept. MP4 is fussy about subtitle formats and awkward with several audio tracks; MKV takes unlimited audio tracks, SRT and ASS subtitles, and chapter markers without complaint. If your MP4 carries two audio tracks and a subtitle stream, all of them survive the move, ffmpeg's default behaviour would keep only one per type, so this tool maps every stream across deliberately.
Convert when a file is heading into a Plex, Jellyfin or Kodi library, when you want commentary and dub tracks kept alongside the main audio, or when you are archiving and want the flexible container. Stay on MP4 for anything going to an iPhone, an Apple TV, PowerPoint or a social platform, those either prefer or require MP4.
MP4 vs MKV: Side-by-side
Technical comparison of the two formats, useful for deciding which to use, or for confirming what changes during conversion.
| Property | MP4 | MKV |
|---|---|---|
| Full name | MPEG-4 Part 14 | Matroska Video |
| Year introduced | 2001 | 2002 |
| Developer / standard body | MPEG | Matroska Foundation |
| MIME type | video/mp4 | video/x-matroska |
| File extension | .mp4 / .m4v | .mkv |
| Compression | H.264 or H.265 codec | Codec-flexible (H.264, H.265, AV1, VP9) |
| Color / data depth | 8/10-bit | Up to 12-bit |
| Max dimensions / size | Codec-dependent (up to 8K) | Codec-dependent |
| Transparency | No | No |
| Animation | No | No |
| Standard / specification | ISO/IEC 14496-14 | Matroska |
| Best for | Universal video compatibility, plays on every device | High-quality video with multiple audio/subtitle tracks |
Use MP4 when
- The video is going to a website, phone, or messaging app
- You want it to play on TVs, browsers, and casual devices
- You're uploading to a streaming platform
- Simplicity matters more than flexibility
Use MKV when
- You're archiving films with multiple audio tracks or subtitles
- You want commentary tracks, dubs, or original audio all together
- You're storing content for a home media server (Plex, Jellyfin)
- You want to keep source-quality codec choices without transcoding
Ship as MP4, archive as MKV. If your video needs to just work everywhere, MP4. If you're building a proper media library with subtitles and multiple audio tracks per film, MKV. Converting between them is usually a remux (container-only swap) that takes seconds, no quality loss.