Question 1

Does converting MKV to MP4 lose quality?

Accepted Answer

Not when the video is H.264, the most common codec in MKV files. It's moved into the MP4 as it is, so the picture is identical and the conversion takes seconds. Other codecs, such as HEVC, VP9 or AV1, are re-encoded to H.264 at a high quality setting so the MP4 plays everywhere.

Question 2

What happens to subtitles and extra audio tracks?

Accepted Answer

The MP4 gets the main video track and the main audio track. Subtitle tracks and extra audio languages are left out.

Question 3

What if the MKV has AC-3 or DTS sound?

Accepted Answer

Browsers can't decode DTS, and many can't decode AC-3. A sound track the browser can't decode is copied into the MP4 when MP4 can hold it, and otherwise left out; the result is then marked No sound.

Question 4

Why convert MKV to MP4 at all?

Accepted Answer

MKV is common for downloads and screen recorders such as OBS, but iPhones, iMovie, many smart TVs and most social sites won't take it. MP4 plays everywhere.

Question 5

Is it free?

Accepted Answer

Yes. Convert as many files as you like and download the results of files up to 200 MB each for free, with no sign-up and no watermark.

Question 6

Are my videos uploaded?

Accepted Answer

No. The MKV is read and the MP4 is written in your browser, so the video never leaves your device.

MKV to MP4 Converter

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Why MKV files don't play everywhere

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