How to use the MKV to MP4 tool
- Choose the video you want to convert.
- Leave "Fast mode" on when it appears: it changes the container without re-encoding, so it is instant and lossless. Otherwise pick a quality.
- Press Convert.
- Preview the result and download it.
About this tool
MKV (Matroska) usually holds H.264, HEVC, VP9, AV1 and more video with AAC, Opus, AC-3, DTS, FLAC audio and is best known for archiving, downloads and screen recording (OBS). Works when the video inside is H.264, HEVC (device dependent), VP8, VP9 or AV1. Audio in AAC, MP3, Opus or Vorbis is handled; audio such as AC-3 or DTS cannot be decoded by most browsers, so the result would have no sound and you will be told.
MP4 with H.264 video and AAC audio is the closest thing to a universal video format. It plays on iPhones, Android phones, Windows, macOS, smart TVs and game consoles, uploads to every social platform, and previews inline in email and chat apps.
Because MKV and MP4 can hold the same codecs, this conversion is usually a rewrap: the video and audio streams are copied into a new MP4 file without being re-encoded. It takes a moment even for large files and the quality is identical. If your file uses codecs that MP4 cannot carry, the tool falls back to a normal re-encode.
Common reasons to convert MKV to MP4
- Making an OBS or screen-recorder MKV play on phones, TVs and in iMovie or Premiere.
- Getting a preview to appear in chat apps and email, which rarely show MKV.
- MKV to MP4 is usually an instant rewrap when the video is H.264 or HEVC and the audio is AAC.
MKV vs MP4 at a glance
| MKV | MP4 | |
|---|---|---|
| What it is | Matroska | MPEG-4 Part 14 |
| Typical video codecs | H.264, HEVC, VP9, AV1 and more | H.264, HEVC, AV1 |
| Typical audio codecs | AAC, Opus, AC-3, DTS, FLAC | AAC, MP3 |
| Best for | Archiving, downloads and screen recording (OBS) | Sharing, social platforms, phones, TVs and email |
| Plays on | PC players such as VLC; few phones and TVs | Practically everywhere |
Why use ToolsCrow for this
- Instant when possible. Rewrap without re-encoding.
- Private. Files never leave your device.
- No watermark. Free, no account.
- Honest errors. Unsupported codecs are explained, not hidden.
Good to know
- Works when the video inside is H.264, HEVC (device dependent), VP8, VP9 or AV1. Audio in AAC, MP3, Opus or Vorbis is handled; audio such as AC-3 or DTS cannot be decoded by most browsers, so the result would have no sound and you will be told.
- Output is H.264 video with AAC audio (or Opus if your browser cannot encode AAC).
Frequently asked questions
Is my video uploaded to a server?
No. Everything runs inside your browser tab using your own device's video hardware. Your file is never sent to ToolsCrow or anyone else, which also means there is no waiting for an upload and it keeps working if your connection drops after the page has loaded.
Is it really free? Is there a watermark?
It is free with no sign-up, no watermark and no daily limits. The only limits are the ones your device sets: memory and processing power.
How large a video can I use?
Because the video is processed on your device, the limit is your device's memory rather than a server quota. Phone clips of several hundred MB are fine on most devices, and desktop computers usually handle 1 to 2 GB. Files over about 4 GB are not supported.
Which browsers work best?
Current Chrome, Edge and Safari (16.4 or newer, including iPhone and iPad) work best because they include the WebCodecs video engine. Recent Firefox versions work for many files. Older browsers fall back to a much slower real-time mode or may not work at all.
Will converting MKV to MP4 reduce quality?
Not in Fast mode: the streams are copied, so quality is identical. If a re-encode is needed, the High preset keeps it visually the same and caps the bitrate so the file does not grow.
What is the difference between MKV and MP4?
MKV is Matroska, best for archiving, downloads and screen recording (OBS). MP4 is MPEG-4 Part 14, best for sharing, social platforms, phones, TVs and email.
Why does my result have Opus audio instead of AAC?
Some browsers (for example Chrome on Linux) cannot encode AAC audio. When that happens the tool saves Opus audio instead and tells you. Opus plays in Chrome, Firefox, Edge, VLC and recent Safari; if you need AAC everywhere, run the tool in Chrome or Edge on Windows or macOS, or in Safari.
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