MP4 for compatibility — phones, browsers and TVs all play it. MKV is better for archiving but poorly supported.

Websites. It is royalty-free and efficient, but less supported outside browsers.

Will converting lose quality?

A little, once. Avoid converting the same file repeatedly, since the loss compounds.

Can I increase the resolution?

No. Upscaling cannot add detail that was never recorded.

Why did my file get larger?

Converting from an efficient codec to a less efficient one at high quality can do that. Lower the quality or pick a smaller resolution.

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Video converter

Convert video between MP4, WebM, MOV and MKV.

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Quality

Resolution

This tool needs JavaScript, because the work happens on your own device rather than on a server. Everything below — the guide and the answers — works without it.

Container and codec are different things

This trips people up constantly. MP4, MKV and MOV are containers — boxes holding video and audio streams. The codec inside decides how those streams are compressed. Two MP4 files can be encoded completely differently, which is why one plays on your TV and the other does not.

Converting here re-encodes the streams and rewraps them, so the result plays reliably rather than merely being renamed.

Choosing a format

MP4 (H.264) — the universal default. Plays on every phone, browser, TV and editor.
WebM (VP9) — royalty-free and efficient, ideal for a website. Less well supported outside browsers.
MOV — Apple's container, what QuickTime and Final Cut expect.
MKV — flexible and popular for archiving, poorly supported by phones and browsers.

Resolution and quality

Downscaling is the most effective single change you can make to file size, and often the least visible: 1080p footage viewed on a phone is indistinguishable from 720p. The quality setting controls how hard the encoder compresses at whatever resolution you choose.

Upscaling is not offered, because enlarging cannot add detail that was never captured.

Converting costs quality, once

Any conversion between compressed formats re-encodes and loses a little. It is usually invisible at the high and balanced settings. What you should avoid is converting the same file repeatedly — each round trip compounds.

Length limit

Fifteen minutes of source, because transcoding must complete inside a single request. Longer videos need trimming first, which is lossless and takes seconds.

Audio is converted too

The audio track is re-encoded alongside the video — AAC for MP4, MOV and MKV, Opus for WebM — at a bitrate suited to the container. If the video has no audio track, none is added. If you want the soundtrack on its own instead, extracting the audio is the tool for that.