MP4 vs MKV
Both are containers holding the same kinds of video inside. MP4 plays on everything; MKV holds more — several audio tracks, subtitles, chapters — but is refused by a lot of players, phones and TVs.
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Choose MP4 when
- Sending video to anyone, or putting it on a phone or a website.
- Editing software and social platforms, which expect MP4.
Choose MKV when
- Films with multiple audio languages or subtitle tracks.
- Archiving, where keeping every track in one file matters.
- Playback on a computer with a decent player like VLC.
What MP4 actually is
MP4 is a container: it holds a video stream, usually H.264, an audio stream, usually AAC, and any subtitles or chapter data, and describes how they line up. Almost every device made in the last fifteen years plays that combination in hardware, which is why MP4 became the default.
Two MP4 files can behave completely differently depending on the codecs inside. A file that will not play is usually an unusual codec in an ordinary container, not a broken file.
What MKV actually is
Matroska will hold essentially any combination of video, audio and subtitle streams, in any codec, in unlimited numbers, with chapters and attachments alongside. That is why it is the format of choice for archived films with several language tracks and subtitle sets.
MKV and WEBM share a signature because WEBM is a restricted Matroska, so tools sometimes report one as the other. What matters is the codecs inside.
MP4 and MKV side by side
| MP4 | MKV | |
|---|---|---|
| Extension | .mp4 | .mkv |
| Media type | video/mp4 | video/x-matroska |
| Compression | Lossless | Lossless |
| Transparency | No | No |
| Animation | No | No |
| Quality setting | Not applicable | Not applicable |
| We can write it | Yes | Yes |
Questions
Does converting MKV to MP4 lose quality?
It does not have to. If the video and audio inside are already MP4-compatible — H.264 and AAC usually are — the streams are copied across untouched and only the wrapper changes. That is why it can finish in seconds.
What happens to my subtitles?
MP4 supports far fewer subtitle types than MKV. Extracting them to a separate SRT file alongside the video is usually the cleaner outcome.