How to Convert MKV to MP4 (Free, Without Losing Quality)

MKV is a popular video format for films, TV recordings and screen recorders. It holds high-quality video, several audio languages and subtitles in one file. The catch: iPhones, many smart TVs, browsers, video editors and social media sites don't open it. MP4 plays everywhere, so converting MKV to MP4 is the usual fix.

Convert MKV to MP4 online

1. Open the MKV to MP4 converter.
2. Drop your videos onto the page, or click Choose Files. Add up to 20 videos, up to 1 GB in total.
3. Click Convert and download your MP4s.

That's it. It works in the browser on Windows, Mac, Linux, iPhone and Android, with nothing to install.

Keep the original quality

MKV and MP4 are both containers: boxes that hold the video, audio and subtitles. Most MKV files already contain video MP4 can hold, usually H.264 or H.265. So the video can be moved into the MP4 box as it is, which is called remuxing.

To do that, click the settings button next to the format and set Video codec to copy. Nothing is re-encoded, so the picture is identical to the original. If the MKV uses another codec (such as VP9 or AV1 from some downloads), leave the default instead: the video is re-encoded to H.264 at high quality, which plays almost everywhere.

Fix a video that plays with no sound

Films in MKV often carry DTS, AC3 or FLAC audio. Many phones, browsers and editing apps can't play those, so the video looks fine but stays silent. Leave the audio setting at its default: the sound is converted to AAC, which every device plays.

Make big videos smaller

MKV films can be several gigabytes. Before converting, open the settings:

• Resolution: 1080p is plenty for most screens; 720p is fine for phones and messaging.
• Quality: a lower value makes a smaller file. Leave it at the default if you're not sure.
• Trim: set a start and end time to keep only the part you need.

Subtitles and extra audio tracks

MP4 can hold several audio tracks and subtitles, but not every MKV track carries over. RunConvert always keeps the main video and audio track. If you need a particular language or subtitle track, check the result before deleting the original MKV.

Don't just rename the file

Changing the extension from .mkv to .mp4 doesn't convert anything. The file is still an MKV inside, and most players will refuse to open it. Use a converter so the video is actually rewrapped or re-encoded as MP4.

Converting many MKV files

Got a whole folder of videos? Drop them all onto the MKV to MP4 converter at once. For very large libraries, the RunConvert CLI converts a folder from the terminal:

runconvert convert ~/Movies --only video --to mp4

Other video formats

The same steps work for other formats: MOV to MP4 for iPhone and Mac videos, MKV to AVI for older players, or the video converter for anything else. Only need the sound? Use MP4 to MP3. For the differences between the two formats, read MKV vs MP4.