What is MKV?
MKV (Matroska Video) is a free, open container format that can hold an unlimited number of video, audio, subtitle and attachment tracks in one file.
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Definition
MKV — MKV (Matroska Video) is a free, open container format that can hold an unlimited number of video, audio, subtitle and attachment tracks in one file. It accepts almost any codec, which makes it popular for archiving movies with several languages, but many phones and editing apps do not open it natively.
What makes MKV different
Matroska started in 2002 as an open project to build a container with no artificial limits. Where MP4 is tuned for broad device support, MKV is tuned for flexibility. One MKV can contain:
- Video in H.264, H.265, VP9, AV1 and many others
- Several audio tracks, for example English, Spanish and a director's commentary
- Multiple subtitle tracks, including styled formats as well as simple SRT text
- Chapters, fonts and cover images as attachments
The WebM format is actually a trimmed-down subset of Matroska.
Why MKV matters when downloading videos
Downloaders sometimes use MKV as a fallback because it can hold any pair of video and audio streams. When a site delivers video and audio separately, the tool has to mux them into one file. If that combination does not fit MP4's rules, MKV is the container that always works.
The catch is playback. VLC, mpv, Kodi, Plex and many smart TVs handle MKV well. The default video apps on iPhone and many Android phones, plus a lot of mobile editors, do not. If you want to share the clip or edit it, an MP4 is usually less hassle.
MKV vs MP4
| MKV | MP4 | |
|---|---|---|
| Codec choice | Nearly unlimited | Narrower list |
| Multiple subtitle and audio tracks | Excellent | Possible but less common |
| Phone and editor support | Limited | Excellent |
Converting MKV to MP4
If the codecs inside an MKV are also allowed in MP4 (H.264 with AAC is the classic case), the file can be remuxed in seconds with no quality loss. If not, it needs transcoding, which is slower and slightly lossy. Our guide on MP4 vs WebM vs MKV explains when each container makes sense.
For files that open straight away on a phone, use SaveVidr's MP4 option. As always, save only videos you are allowed to keep.
FAQ
Frequently asked questions
Is MKV better quality than MP4?
No. MKV and MP4 are just containers, so the same video stream looks identical in either one.
Why won't my phone play an MKV file?
Many built-in phone players do not support the MKV container; a player such as VLC, or converting to MP4, usually solves it.