MKV to MP4
Convert MKV to MP4 so the video plays on an iPhone, a TV, in an editor or on a website. Most files are moved across in seconds with nothing lost.
How the files you choose are handled is set out in the privacy policy.
How to convert MKV to MP4
- Tap Choose a video and pick the MKV file.
- Read the line under the settings. It says whether the video will be copied or converted, and what happens to the sound.
- Press Convert to MP4, then save the result.
Why MKV files will not play
MKV, short for Matroska, is a flexible container that can hold almost any kind of video and sound, many audio languages and many subtitle tracks at once. That flexibility is why it is popular for films and recordings, and also why support is patchy. iPhones, iPads, many smart TVs, most video editors and nearly every upload form expect MP4 and turn MKV away.
The video inside is usually perfectly ordinary. It is only the wrapper that is the problem.
Usually nothing is re-encoded
Most MKV files hold H.264 video, the same kind MP4 files use. For those, converting means lifting the video out of one container and placing it in another. It takes seconds even for a long film, and the picture is bit for bit the same.
| Inside the MKV | What happens | Quality |
|---|---|---|
| H.264 video | Copied | Identical |
| HEVC (H.265) video | Your choice: keep it, or convert to H.264 | Identical if kept |
| VP9 or AV1 video | Your choice: keep it, or convert to H.264 | Identical if kept |
| AAC or MP3 sound | Copied | Identical |
| Opus, Vorbis or FLAC sound | Converted to AAC | Very close |
| Dolby Digital (AC-3) or DTS sound | Cannot be converted here | The MP4 has no sound |
What an MP4 cannot take with it
- Extra audio tracks. An MKV with several languages keeps the first one.
- Subtitles. Subtitle tracks are left out. If the subtitles are separate .srt files, keep them beside the MP4 under the same name and most players pick them up.
- Chapters and attachments, such as embedded fonts and cover pictures.
Films with Dolby or DTS sound
Many film rips carry Dolby Digital or DTS audio. Browsers cannot decode those, so they cannot be turned into the AAC that MP4 players expect. The tool warns you before you start, and if you go ahead the MP4 will be silent. For such files, a desktop program such as HandBrake or VLC is the right tool.
Afterwards
If the MP4 is too large to send, the video compressor makes it smaller. To cut out a scene, use the video trimmer. Other source formats are handled by the general MP4 converter.
Questions
Does converting MKV to MP4 lose quality?
Not when the video is H.264, which is the usual case. It is copied exactly. Only video you choose to convert to H.264 is re-encoded.
Why is the conversion so fast?
The video is moved into a new container without being re-encoded, so even a long film takes seconds.
Why does my MP4 have no sound?
The MKV used Dolby Digital or DTS audio, which cannot be converted in a browser. The tool warns about this before converting.
Are subtitles kept?
No. Subtitle tracks, chapters and extra audio tracks are left out. One video track and one audio track are carried over.
Is there a file size limit?
No fixed limit when the video is copied. Converting to H.264 depends on your device and takes longer for long videos.
Related converters and guides
- MP4 converterConvert MOV, MKV, WebM, M4V and 3GP videos to MP4.
- WebM to MP4Turn WebM recordings and downloads into MP4 that plays anywhere.
- Video compressorMake a video small enough to send or post. Pick a quality, or a size such as 16 MB.
- MOV to MP4Turn iPhone, camera and QuickTime MOV files into MP4, usually with no quality loss.