Is MKV higher quality than MP4?

No, this is a common misunderstanding. Quality follows the video codec and bitrate inside, not the container. The same H.264 stream gives exactly the same picture inside an MKV as it does inside an MP4. The reason MKV files sometimes look better is that high-bitrate content has traditionally been distributed as MKV, not the container itself.

Why should I convert instead of just playing the MKV directly?

If MKV opens without problems on the device you watch on, you do not need to convert. The need to convert generally arises when smart televisions, games consoles, older phones or video editing programs come into play; many of these do not recognise MKV. Likewise most social media platforms and web upload forms expect MP4. Converting is therefore a decision made according to where the file is going.

What happens to the subtitles inside an MKV?

That depends on the type of subtitle. MKV can carry text-based SRT and ASS subtitles as well as image-based PGS subtitles; MP4 does not carry that whole range in the same way. Text subtitles can usually be converted into a format MP4 supports, though complex positioning and styling information in ASS may be simplified. With image-based subtitles the track is either dropped or has to be burned permanently onto the picture.

Can MKV's multiple audio tracks be carried over to MP4?

MP4 can technically carry more than one audio track, but there are two obstacles in practice. First, the audio codec in the MKV has to be compatible with MP4; some codecs such as DTS cause problems and need to be encoded. Second, many players do not offer audio track switching inside MP4 as comfortably as they do with MKV. That is why most conversion flows take only one audio track by default, so it is worth knowing in advance which one will remain.

What Is MKV and Why Does Everyone Keep Converting It to MP4?

MKV is not actually a video format

That sentence may sound odd at first, but nearly all of the confusion around MKV is resolved right here. The .mkv extension tells you nothing about how the picture inside the file was compressed. It only tells you which container was used.

MKV's full name is Matroska. It comes from the Russian matryoshka dolls, and the name is no accident: it describes structures that nest inside one another. It is an open-source container, owned by no company, and designed to be able to carry almost anything.

What can it contain? Video codecs such as H.264, H.265, VP9, AV1; audio codecs such as AAC, MP3, AC3, DTS, FLAC, Opus; different kinds of subtitles such as SRT, ASS, PGS. All at the same time, all in multiple copies.

What makes MKV so powerful

Matroska's design goal from the very beginning was to be a container that does not impose limits. The practical consequences are quite striking:

A near-unlimited number of tracks. A single MKV file can carry five audio tracks, eight subtitle tracks and more than one video track at once. You can keep a film in one file with its original language, its Turkish dub, a commentary recording and subtitles in six different languages.

No fussiness about codecs. While MP4 has essentially standardised around a particular family of codecs, MKV accepts almost anything. When a new codec appears, MKV is usually among the first containers to carry it.

Chapter markers and rich metadata. You can define chapters within a video and give each track a label and language information.

A structure more resilient to damage. MKV was designed with the idea that the rest of a file should remain playable even if part of it is corrupted.

Open and free. Because there is no licensing obstacle, it is comfortably supported by free software.

So why is everyone moving to MP4?

All that flexibility in MKV comes at a price: device support.

MP4's greatest strength is that you know from the outset what to expect. When a device manufacturer adds MP4 support, it knows the files it will encounter will most likely carry H.264 or H.265 video and AAC audio. Thanks to that predictability, hardware decoders are built directly for that scenario.

There is no such guarantee with MKV. What will turn up inside an MKV file is not knowable in advance, and that makes it hard for every device to support it. The upshot:

Many smart televisions either do not open MKV at all, or open it but do not play the audio
Games consoles and media players offer limited support
iPhone and iPad do not open MKV in the default player
Most video editing programs will not import MKV directly
Social media platforms and web upload forms generally want MP4
Playing directly in a browser with the <video> tag is not reliable for MKV

So MKV is perfect for archiving and watching on a computer; it is problematic for sending to someone else, uploading somewhere, or opening on a television.

The most important part: conversion usually costs no quality

This is the point that most articles about moving from MKV to MP4 skip over.

If the MKV file you have contains H.264 or H.265 video and AAC audio — and a very large proportion of the MKV files in circulation today do — moving to MP4 requires touching the picture not at all. The video and audio data is taken out of the Matroska container and copied into the MP4 container as it is.

This operation is called a remux and it has two properties: quality loss is zero, because no bit changes; and it is fast, because the compression algorithm never runs.

This means the answer to "will the quality drop if I turn my MKV into an MP4" is in most cases a firm "no". That knowledge alone prevents people from spending hours re-encoding at needlessly high bitrate settings.

When is a remux not possible?

To be honest, not every MKV is that easy. In the following situations the picture or the tracks have to be processed:

If the video codec is incompatible with MP4. If the MKV contains VP9 or some older/rare codecs, MP4 will not carry them reliably. The picture has to be re-encoded to H.264 or H.265, and that operation is a genuine compression — some quality loss occurs. On a long film this takes minutes.

If the audio codec is incompatible. Some audio formats such as DTS are problematic in the MP4 container. In that case the audio is encoded to AAC. Because the picture is not touched there is no visual loss, and the loss on the audio side generally goes unnoticed in everyday listening.

If the subtitles cannot be carried. MKV's image-based subtitles such as PGS do not pass directly to MP4. These tracks are either dropped or burned permanently onto the picture — the second option requires re-encoding.

If there is more than one audio track. Most conversion flows take only one of them. It is worth checking the source in advance so you do not end up with a file where the original language remained instead of the Turkish dub.

If you do not know what codec is inside, there is no need to worry — our MKV to MP4 conversion tool reads the file and prefers the lossless route where possible.

Which to use when?

A simple distinction will serve you: MKV to keep, MP4 to send.

If you are archiving a film with multiple audio and subtitle tracks, and watching it on your computer with a player such as VLC, MKV gives you more. If you are going to open the same file on a television, put it on a phone, upload it somewhere or bring it into an editing program, MP4 is the right choice.

In summary

MKV is not a bad format; on the contrary it is technically more capable than MP4. Its problem is not incapability but the exact opposite, being too flexible: device manufacturers struggle to support it because they cannot know what they will encounter. MP4, by contrast, promises little and keeps that promise everywhere. And the good news is that moving between the two is most of the time an operation that never touches the picture and amounts to changing the box.