MKV files: the container that holds everything, and plays nowhere
Why MKV files carry multiple audio tracks and subtitles, why televisions refuse them, and what survives a conversion. Convert MKV in your browser, no upload.
At a glance
- Type
- Video
- Container format
- Yes
- Extensions
- .mkv
- MIME type
- video/x-matroska
- Common codecs
- h264, h265, vp9, av1, flac, aac
- Also known as
- Matroska
Matroska — MKV — was designed in 2002 to be the container that never says no. It holds any number of video tracks, any number of audio languages, soft subtitles in several formats, chapter markers, attached fonts, and essentially any codec. That openness is why film and series releases use it: everything from the source disc can be kept in one file, with the viewer choosing language and subtitles at playback.
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It is also why so little will play it. MKV never entered the broadcast or mobile standards, so hardware decoders and smart TV firmware largely do not implement it, and neither do most browsers. The video inside is usually perfectly ordinary H.264 or HEVC — the wrapper is what the device refuses. That mismatch is the entire reason MKV to MP4 is one of the most-wanted conversions there is.
Converting to MP4 is a repack: the video and audio streams are copied across untouched, so it takes seconds and the picture is bit-for-bit identical. All audio tracks come across, so a release with an original and a dubbed track keeps both. Subtitles do not — MP4 accepts almost none of the subtitle formats MKV carries, ASS in particular, whose positioning and styling MP4 has no way to express. They are left out rather than failing the job.
Going the other way has its uses. Converting MP4 to MKV is the move when you are assembling rather than distributing: adding a second audio track, attaching a subtitle file, marking chapters. Do the repack first and the later steps never touch the video itself.
Convert MKV to other formats
Convert other formats to MKV
FAQ
Why will my TV not play MKV?
Because MKV never became part of the broadcast and mobile standards, so most hardware decoders and TV firmware do not implement it. The video inside is usually ordinary H.264 — it is the container being refused.
Does MKV to MP4 lose quality?
No. The streams are copied without being decoded, so the result is identical to the source. Only asking for a different resolution or quality forces a real re-encode.
What happened to my subtitles?
They were left out, because MP4 cannot carry the SRT and ASS formats MKV uses. Extract them separately with a tool like MKVToolNix and keep the .srt next to the MP4 — most players load a matching file automatically.
Are all the audio tracks kept?
Yes. Every audio track is carried across, so a file with original and dubbed audio keeps both and you can switch between them in your player.
Which audio track do I get if I extract audio?
The first one, which is what your player would choose by default. Selecting a specific track is not offered here; MKVToolNix can extract a chosen track without re-encoding.
Why convert to MKV at all?
Because it accepts things MP4 does not — multiple languages, soft subtitles, chapters, attached fonts. It is the container to assemble a file in, even if you repack to MP4 afterwards for playback.
How large an MKV can this site handle?
About 667 MB for a container swap, since output and input are the same size and both share the converter's memory. Films frequently exceed that; for those a desktop tool is the practical answer.
Is MKV better than MP4?
More capable, not better. MKV holds more; MP4 plays more places. Which one is right depends entirely on whether you are storing the file or handing it to a device.