MP4 vs MKV: which should you use?
Both are containers. MKV can hold almost anything: many audio languages, subtitles, chapters. MP4 plays on almost anything. We rewrapped one video both ways to compare.
- Never uploaded
- No size limit
- No watermark
- Free
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Quick answer: With the same video inside, MKV and MP4 are the same size and quality: our 52-second 1080p test was 14.61 MB as MKV and 14.62 MB as MP4, with bit-identical video. MKV holds more: several audio tracks, subtitle tracks and chapters. MP4 plays on more devices, including iPhones, most TVs and editors. Keep MKV for films with many tracks on a computer or Plex; use MP4 to share or play on phones.
Updated
Choose MP4 when
- It has to play on an iPhone, an iPad, a TV, a games console or in an editor.
- You share or upload the video.
- You want Plex or Jellyfin to play it directly on more devices, without converting on the fly.
Choose MKV when
- A film has several audio languages or subtitle tracks you want to keep in one file.
- You archive, and every track matters.
- You play it on a computer with VLC or a media server.
The same video in each wrapper
| Container | Size | Video inside |
|---|---|---|
| MKV | 14.61 MB | H.264, identical (MD5 checked) |
| MP4 | 14.62 MB | H.264, identical |
| MOV, for comparison | 14.62 MB | H.264, identical |
The 52-second 1080p Sintel trailer (H.264 video, AAC sound), rewrapped without re-encoding on 20 October 2026. Sintel © Blender Foundation, CC BY 3.0.
How it works
- Drop your videoThe file is read on your computer, never uploaded.
- ConvertMany videos convert in seconds with no quality loss; the rest are converted at high quality.
- Download the MP4Plays on Windows, Android, iPhone, Mac and every website.
Why an MKV plays without sound
Films in MKV often carry AC-3, E-AC-3 or DTS surround sound, which many TVs, browsers and phones cannot decode: the picture plays in silence. Converting to MP4 here turns that sound into AAC, which plays everywhere. See MKV has no sound.
What converting keeps
Ordinary H.264 video is copied across untouched, so the conversion is quick and loses nothing; other video codecs, and HDR video, are re-encoded to H.264. The MP4 gets the main video and sound track: extra audio languages and subtitle tracks are left out, so keep the MKV if you need them.
Measured, not promised
From our tests on a 2019 Intel MacBook, an Apple M1 and a Windows PC without a graphics card. See all results.
Why your video never leaves your computer
Online video tools upload your file to their servers, process it there, and send it back. That is slow for big videos and costs them money for every minute, so free plans cap your file size or add watermarks, and your video sits on someone else's computer.
Here your own computer does the work, inside this tab. Nothing is uploaded, so there is nothing to cap: no file size limit, no daily limit and no watermark.
Questions
Does converting MKV to MP4 lose quality?
Not when the video is ordinary H.264: it is copied, not re-encoded. Other codecs and HDR video are re-encoded at high quality. Extra audio languages and subtitles are not carried over.
Is MKV better quality than MP4?
No. With the same codec inside they are identical, as our test shows.
MP4 or MKV for Plex and Jellyfin?
Both work. MP4 plays directly on more TVs and browsers, so the server has to convert less often.
Can I convert several files at once?
Yes. Choose or drop several files together. They are converted one after another with the same settings, and you can download each one or all of them in one ZIP.
Is it really free?
Yes. Your computer does the work, so a video costs us nothing to process. No account, no watermark, no limits.
Is my video uploaded?
No. It is processed inside this browser tab and saved straight back to your computer.
Which browsers work?
Recent Chrome, Edge and Safari on a computer. Chrome and Edge are fastest on most machines. Phones work for short videos.
How long does it take?
In Chrome, a one-minute 1080p video took 13–19 seconds on the laptops we tested and about 40 seconds on a computer without a graphics chip. Safari can be slower.
Can I close the tab while it works?
Keep the tab open and in front until it finishes. Browsers slow down background tabs.