Video Converter

How it works

A video file has two layers: the container (MP4, MKV, MOV, WebM), which is like a box, and the codecs inside it that compress the picture and the sound. When you only need a different box — for example an MKV with H.264 and AAC that a phone wants as an MP4 — the tool moves the picture and sound into the new container without touching them. That takes seconds and loses nothing. Otherwise it re-encodes the video, which lets you change the size and quality but takes much longer.

The work is done by ffmpeg compiled to WebAssembly. That engine is about 31 MB. It is downloaded only when you press Convert video, checked against a known fingerprint, and stored in your browser, so the next time it starts at once. It runs in the background, so the page stays responsive, and you can press Cancel at any time.

How long does it take?

Re-encoding in a browser uses one processor thread, so it is much slower than a desktop program: roughly half of real time for 720p video and a quarter of real time for 1080p. The page shows an estimate before you start, based on the picture size, frame rate and length, and warns you when it is more than about five minutes. To make it faster, choose a smaller size, or use Trim & Cut Video first to keep only the part you need. HDR videos take about five times longer because of the tone mapping.

Formats and quality

MP4, MKV and MOV are saved with H.264 video and AAC sound. WebM is saved with VP8 video and Vorbis sound; the newer VP9 codec is not offered because it does not run reliably in the browser engine. The quality settings are High (large, very close to the original), Balanced (a good default) and Small file (visibly softer, much smaller). The size option never enlarges a video.

HEVC, HDR and iPhone videos

Videos from an iPhone are usually MOV files that use HEVC (H.265), and often HDR. HEVC can be read and converted here, but many browsers cannot play it in the preview, so the preview may stay black even though the conversion works. HDR videos are converted to standard dynamic range with tone mapping; colours and brightness can differ a little from what an HDR screen shows. If you would rather keep HDR, choose Just change the container, which keeps everything as it is. If a file uses something the engine cannot decode, the page says so instead of failing silently.

Frequently asked questions

Is my video uploaded?

No. The only download is the conversion engine itself. Your video is opened directly from your disk and never sent anywhere.

Will it work with protected videos?

No. Videos protected by copy protection (DRM), such as many downloaded films or streaming-service files, cannot be read. Only use videos you have the right to use.

What are the limits?

The limits are shown at the top of the page. The finished file is built in memory before you can save it, so on a phone or an older computer choose a smaller video if the tool reports that it ran out of memory.

Related tools: Trim & Cut Video, Mute Video, Extract Audio from Video.