Live
MOV → MP4
Make a QuickTime MOV play everywhere
MKV to MP4
LivePut the video from an MKV into an MP4 that phones, TVs, browsers and editing software will open. An MKV that already holds H.264 or HEVC keeps its picture exactly as it is: the encoded video is copied across, not compressed again. The soundtrack is the part that usually has to change, and the result screen says which of the two happened to your file.
What it does
- Copies the picture across untouched when MP4 can carry it, so the quality does not move
- Re-encodes AC-3, DTS or Opus sound to AAC and leaves the picture alone
- Takes the first video and audio track only: extra languages and subtitles are left behind
Your files
Gone within the hour.
Files are uploaded over HTTPS, used only to run this tool, and deleted from our server automatically about an hour later. Never sold, never used to train anything.
How to convert an MKV to MP4 without losing quality
Drop the MKV in
Use the box above, or click it to browse. One file per job, up to 50 MB, and up to 20 minutes of running time. If your browser cannot preview the file, that is normal and is usually the reason you are here: the server reads it with ffmpeg either way.
Leave the quality setting alone if you can
The three choices, Higher quality, Balanced and Smaller file, are only consulted if the picture has to be re-encoded. On an MKV holding H.264 or HEVC they are never used, because nothing is re-compressed.
Press Convert to MP4
A file whose streams are simply moved into the new container finishes in about a second. One whose picture has to be encoded again, VP9 and AV1 being the usual reasons, takes roughly as long as the video is.
Read what it says it did
The result screen reports whether anything was re-encoded, taken from the job itself rather than assumed. Nothing was re-encoded means the video in your MP4 is byte for byte the video in your MKV.
Frequently asked questions
Does converting MKV to MP4 lose quality?
Not to the picture, in the ordinary case, and that is worth being precise about rather than reassuring. MKV and MP4 are containers: boxes around already-encoded streams. When an MKV holds H.264 or HEVC video, which most of them do, the encoded video is lifted out and put into the MP4 without being decoded, so the picture in the result is the same data that was in the MKV. Measured on 2026-09-20 with a generated H.264 MKV: the video stream came out identical, and the file went from 336,484 bytes to 338,574 because an MP4 index is slightly larger than a Matroska one. What can lose quality is the sound, and the next answer is about that.
Why did it say part of my file was re-encoded?
Almost always because of the soundtrack. MKV files commonly carry AC-3, DTS or Opus audio, none of which an MP4 player can be relied on to open, so that track is encoded again as AAC at 192 kbps while the picture is copied across untouched. Measured on 2026-09-20 with an H.264 and AC-3 MKV: the video stream was identical in the result and only the audio differed. The other reason is the picture itself: a VP9 or AV1 MKV, which is what a downloaded stream often is, has to be re-encoded to H.264, and then the result can be bigger than the file you uploaded. A generated VP9 and Opus MKV went from 80,902 bytes to 118,155 for exactly that reason.
What happens to the second audio track and the subtitles?
They are not carried into the MP4, and no converter that promises otherwise in one click is being straight with you. The job takes the first video track and the first audio track and nothing else, so a film with an English and a Japanese track comes back with only the first one, soft subtitle tracks are dropped, and chapter marks go with them. Track names, the title stored in the container and any device or software name are stripped too. Measured on 2026-09-20: a two-audio, one-subtitle MKV came back with one audio track, no subtitle track, and its language tag reset to undefined.
Will the MP4 play on my phone, my TV and in my editor?
That is the whole point of the tool, and it is why we do not simply repackage whatever ffmpeg will accept. ffmpeg will happily put VP9, Opus, FLAC or AC-3 inside an MP4 and report success, and the file it produces is valid and still will not open on a TV or in an older Windows player. So anything outside a deliberately narrow list is re-encoded: H.264 at 8-bit 4:2:0 for the picture and AAC for the sound. Video recorded in HEVC is the exception, copied across as it is with the tag Apple devices expect, because re-encoding it would throw away detail for nothing.
How big and how long can the MKV be?
One file per job, up to 50 MB, and up to 20 minutes of running time, with the finished MP4 also having to come in under 500 MB. The size limit is the one people meet first, because MKV is the container films arrive in and a film is rarely under 50 MB. There is no daily allowance on this tool and no queue to wait in.
What if my file is an MKA, or is not really a video?
An MKA is a Matroska file with sound and no picture, and it is refused with a message saying so rather than being converted into a video with a blank screen: use Video to Audio if what you want is the sound on its own. A file that is not a media file at all is rejected before it is even uploaded in full. Your MKV and the MP4 it produces are both deleted from our server automatically about an hour later.