Can I convert MKV to MP4 in the browser?

Often yes, when the streams are H.264 or a codec the browser can decode. If the tool cannot write the destination, it uses the server encoder and says so.

Why does conversion take longer than a trim?

A lossless trim can copy frames. A format or codec change has to decode every frame and encode them again.

MP4 or MOV for Apple devices?

MP4 with H.264 and AAC plays on iPhone, iPad and Mac without a special player. MOV is fine as a camera original; it is a worse sharing format.

Guides

How to convert a video without guessing the settings

Turn MOV, WebM, MKV or an older camera file into an MP4 (or GIF, or audio) with a destination preset, a trim, and an honest note about when the file leaves the browser.

Updated 2026-09-21

Conversion is rarely “pick a format and hope.” A phone MOV, a desktop WebM and an MKV from a recorder can all become an MP4, but the useful questions are where the file will play, whether you need the whole timeline, and whether the destination cares about codec, not just the letters after the dot.

Batonbox Convert Video includes destination cards (Web, phones, short-form platforms, email, GIF, MP3), a live preview, and a trim before you run. Common formats encode in the tab. Camera, disc and broadcast containers the browser cannot write go through the server FFmpeg encoder.

Container versus codec, again

MP4 is a box. Inside it you almost always want H.264 (AVC) video and AAC audio if the file has to play in a browser, a slide deck or a messaging app. HEVC (H.265) makes a smaller file on the same picture, but many browsers and editors still refuse it. WebM is VP9 or VP8 in a different box — fine for the web, awkward in older editors.

Renaming .mov to .mp4 does nothing. The streams have to be remuxed or re-encoded. A remux that only changes the box is fast and lossless; a codec change is a new encode.

Presets beat raw codec lists

If you know the destination — a YouTube upload, an Instagram story, a WhatsApp chat, an email — use that card. It sets a size and codec people on that surface can actually play. Leave “pro” codecs alone unless you already know you need HEVC or a broadcast wrapper.

Trim first when you only need a minute of a long recording. Encoding a two-hour file to throw away 110 minutes is a waste of time and quota.

When the file is uploaded

The browser can read and write MP4, MOV, WebM and MKV for most everyday jobs. AVI, WMV, MPEG, FLV, 3GP and a few disc or camera wrappers are sent to the server encoder. That is a real upload, size-capped, and it is the honest path for those formats — not a silent exception.

Step by step

1
Choose the destination, not just the extension
Web or slides: MP4 / H.264. A phone camera roll: MP4. A tiny loop: GIF. Soundtrack only: MP3 or M4A via extract if you do not need the picture.
2
Trim on the preview
Play the clip, set in and out, then convert. The size estimate updates with the range.
3
Leave codec on auto unless you must not
Auto writes H.264 for MP4 and VP9 for WebM. Pick HEVC only when the receiver asked for it by name.
4
Check the first and last seconds
Confirm audio is present if you wanted it, and that a vertical clip did not get letterboxed unless you asked for a landscape frame.

Questions

Can I convert MKV to MP4 in the browser?: Often yes, when the streams are H.264 or a codec the browser can decode. If the tool cannot write the destination, it uses the server encoder and says so.
Why does conversion take longer than a trim?: A lossless trim can copy frames. A format or codec change has to decode every frame and encode them again.
MP4 or MOV for Apple devices?: MP4 with H.264 and AAC plays on iPhone, iPad and Mac without a special player. MOV is fine as a camera original; it is a worse sharing format.