About MKV (Matroska Video)
MKV — Matroska Video — is the container for people who care more about what a file can hold than where it can play. Fully open and endlessly flexible, it accepts virtually any video and audio format, plus multiple audio tracks, chapter marks, and soft subtitles. That is why OBS records to it (an MKV survives a crash mid-recording; an MP4 often doesn’t), and why it dominates the archiving and rip-management world.
The trade-off is reach. Phones, TVs, browsers, and editing timelines largely pretend MKV doesn’t exist. The standard fix is not to touch the video at all but to move it into an MP4 box — and because MKV files very often hold MP4-compatible video, that conversion here is usually a lossless repackage that finishes in seconds.
Convertmaxxing reads MKV and converts it out; it doesn’t create MKV files. One honest limitation: MP4 is a far stricter container, so only the primary video and audio track make the trip — extra languages and subtitle tracks stay behind.
Strengths
- Holds practically any codec, plus multiple audio tracks, chapters, and subtitles
- Crash-resilient recording — the reason OBS defaults to it
- Fully open standard with no licensing baggage
- Usually converts to MP4 losslessly — the video inside is often already compatible
Limitations
- Very limited playback support on phones, TVs, consoles, and the web
- Editing software support is inconsistent at best
- Its multi-track riches don’t survive conversion to stricter containers like MP4
- Creating MKV files isn’t supported here — converting out of MKV is the common need
Why OBS records MKV and recommends converting afterwards
An MP4 keeps its index — the table telling a player where every frame lives — and that index is finalised when recording stops cleanly. If OBS crashes, the power fails, or the disk fills mid-recording, the index is never written and you are left with a file most players treat as corrupt, despite the video data sitting there intact. Anyone who has lost a three-hour stream this way remembers it.
Matroska writes its structure incrementally as it goes, so a recording interrupted at any point is still a valid file up to the moment it stopped. This is precisely why OBS defaults to MKV and offers a "Remux Recordings" option afterwards: record into the crash-resilient container, then repackage to MP4 for editing and sharing once you know the recording survived. That remux is the same lossless container swap this converter performs.
What gets left behind when you convert to MP4
Matroska was designed to hold everything: a film with an original audio track and three dubs, a commentary track, soft subtitles in a dozen languages, chapter markers, cover art, and attached fonts for subtitle styling. MP4 supports a much narrower set, and the tracks that have nowhere to go simply do not make the journey.
In practice, conversion here carries the primary video track and the primary audio track. Additional audio languages, subtitle tracks, and chapter data are dropped rather than silently mangled. If those matter — a film you want to keep with its subtitles and multiple audio options — MKV is the correct container to keep it in, and converting is the wrong move. Convert when you need playback on a device that refuses MKV, and keep the original as your archive copy.
Frequently asked questions
- Does converting MKV to MP4 lose quality?
- Usually none at all. MKV very often contains H.264 or HEVC video with AAC audio, which is exactly what MP4 accepts, so the streams are copied across untouched and the conversion is a pure container swap. Quality is only affected if the video inside uses a codec MP4 cannot carry and a re-encode is genuinely needed — the converter tells you which path it took.
- What happens to my subtitles and extra audio tracks?
- They are not carried over. MP4 has far more limited support for multiple tracks than Matroska does, so conversion keeps the primary video and audio and leaves the rest behind. If subtitles or alternate audio languages matter, keep the MKV as your master and treat the MP4 as a playback copy.
- Why will my TV or phone not play MKV files?
- Because MKV support has to be implemented deliberately and most consumer devices never bothered — the format grew up around desktop players and archiving rather than mainstream distribution. The video inside is often perfectly playable; it is the container the device refuses. That is exactly why a lossless rewrap to MP4 usually fixes the problem in seconds.
- Can I convert a video into MKV here?
- No, MKV is read-only on this site. The overwhelming real-world need runs the other way — people have MKV files that will not play and want something that does. If you need to create MKV files, MKVToolNix is the standard desktop tool for the job.