OneTaskBy Tim King · Updated
MKV to MP4
Remux or Convert Matroska Video, No Upload
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How the MKV To MP4 works
This MKV to MP4 converter turns an MKV file into an MP4. When the video inside is H.264, it is copied across untouched, which is quick and lossless. Other video codecs are converted to H.264. The MP4 then plays on iPhones, smart TVs, editors and upload forms that refuse Matroska. Nothing is uploaded.
MKV to MP4: what changes
Matroska, the format behind .mkv files, appeared in 2002 as an open container that can hold almost anything: any video codec, any number of audio tracks, subtitles, chapters and attachments. That flexibility is why it is popular for recordings and archives. It is also why many devices refuse it. MP4 is stricter and far more widely supported. Converting moves the main video and sound into an MP4. They are copied when MP4 accepts them as they are and re-encoded when it does not.
What is copied and what is converted
- H.264 video is copied without re-encoding. The picture is identical and the conversion takes seconds.
- HEVC, VP9 and AV1 video is converted to H.264, since many players cannot play those codecs inside MP4.
- AAC sound is copied. Opus, Vorbis, FLAC and MP3 sound is converted to AAC.
- AC-3, E-AC-3 and DTS sound, common in film rips, decodes only in some browsers. When the browser cannot decode it, the video is kept, the sound is dropped and the page says so.
What is left out
MP4 can carry only part of what MKV holds, and this page keeps the main video and sound track. Subtitle tracks, extra audio languages, chapters and attachments such as fonts are not copied. OBS recordings with several audio tracks keep the first.
Speed and memory
Copying runs about as fast as the file can be read. Converting uses the device's video hardware through WebCodecs, the browser's video interface. The new file is built in memory, so a computer handles files of several gigabytes but a phone is best kept to a few hundred megabytes.
FAQ
Is MKV to MP4 lossless?
Yes, when the MKV holds H.264 video and AAC sound: both are copied exactly, and the results panel shows "copied without re-encoding". Other codecs are re-encoded at a high quality setting, which loses very little.
Why is my MP4 silent?
The MKV's sound was in a codec this browser cannot decode, usually AC-3 or DTS. Safari decodes AC-3 and E-AC-3 on Apple devices; Chrome and Edge usually do not. Try Safari, or convert the sound with a desktop tool.
Are subtitles kept?
No. Only the main video and sound tracks are written to the MP4. Extract subtitles separately if you need them, for example as an SRT file, and load it alongside the MP4 in your player.
Is the file uploaded?
No. The conversion runs in this browser tab and the file never leaves your device. The page only needs the internet to load itself and the converter library, and the finished file is saved straight from memory to your downloads.
See also: all Audio & Video tools, Units, Images, Documents, Data & Code.
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