Video Converter
- Free
- No upload
- No watermark
Quick answer
A video converter changes a clip from one format to another — MP4, WebM, MOV, MKV or AVI. Pick your output and this tool transcodes the file entirely in your browser with ffmpeg.wasm; nothing is uploaded. The engine is a one-time ~10 MB download on first use, then cached. H.264 in an MP4 is the safest universal target, and because it runs single-threaded, short clips convert fastest.
Step by step
How to video converter
- 01
Add your video
Drag an MP4, WebM, MOV, MKV or AVI file onto the drop zone, or browse for it. The engine reads the real container and codec from the file, not just the extension.
- 02
Choose the output format
Pick your target container — MP4, WebM, MOV, MKV or AVI. MP4 with H.264 is the default for the widest device and browser support.
- 03
Convert and download
The engine transcodes locally and hands you the finished file. On first use it fetches the ~10 MB engine once, then every later conversion runs offline.
In depth
Container vs. codec — what are you actually converting?
This is the one idea that makes video formats click. A container is the outer file — the .mp4, .webm or .mkv wrapper that holds the video, the audio and any subtitles together. A codec is the algorithm the video inside is encoded with — H.264, VP9, AV1. The extension names the container; it does not tell you the codec. That is why an .mp4 and a .mov can hold the very same H.264 video, and why "converting" sometimes means only rewrapping and sometimes means fully re-encoding the picture.
| Container | Common codec inside | Device support | Best for |
|---|---|---|---|
| MP4 | H.264 / H.265 | Universal — every phone, browser, TV | Sharing anywhere, the safe default |
| WebM | VP8 / VP9 | All modern browsers; weak on Apple/apps | Open-format <video> on the web |
| MOV | H.264 / ProRes | Apple-native; fine on Windows too | iPhone and QuickTime footage |
| MKV | H.264 / H.265 / VP9 | PC players (VLC); poor on devices/TVs | Flexible archives, multiple tracks |
| AVI | MPEG-4 / older codecs | Legacy players; large files | Old camera and DivX rips |
Does converting re-encode the video or just rewrap it?
It depends on whether the codec has to change. Going from MOV to MP4 when both hold H.264 is a re-mux — the video stream is copied bit-for-bit into a new container, which is fast and lossless. Going from MP4 to WebM means the picture must be re-encoded from H.264 to VP8, which takes real compute and is generation-lossy. This converter picks the quick path when it safely can and re-encodes only when the target codec demands it.
How fast is in-browser conversion, and how big can the file be?
Be realistic: the engine is ffmpeg compiled to WebAssembly and it runs single-threaded, so it is slower than the ffmpeg on your desktop that uses every CPU core and your GPU. A re-mux is near-instant, but a full re-encode of a few minutes of HD can take a few minutes and will spin your fan. Because the whole file is held in browser memory, very large inputs (multi-gigabyte, long recordings) can exhaust the tab. Short clips are the sweet spot; for anything big, compress the video first or trim it down.
Is my video uploaded to convert it?
No. The file is read, decoded and re-encoded inside your browser and never sent to a server — which is also why there is no upload wait on a large clip. You can verify it: open DevTools, switch to the Network tab, and run a conversion. Apart from the one-time engine download, no request carries your video out. That matters for private recordings, unreleased footage and client work.
Related video tools
For a specific pair there are dedicated pages: MP4 to WebM, WebM to MP4, MOV to MP4, MKV to MP4 and AVI to MP4. If your goal is a smaller file rather than a new format, use compress video. You can also extract the audio as MP3 or add subtitles to the result.
Your files never leave your device
Processed locally in your browser — nothing is uploaded. You can verify it yourself: open your browser’s developer tools, watch the Network tab, and use the tool — no upload request is ever made.
- No file is ever uploaded to a server
- Works offline after the first visit
- No account, no watermark, no limits
A little more clarity
Frequently asked questions
01What is the best format to convert a video to?
MP4 with the H.264 codec, for almost every purpose. It plays on iOS, Android, Windows, macOS, browsers and TVs. Choose WebM only when you specifically want an open format for web `<video>`.
02What is the difference between a container and a codec?
The container (.mp4, .webm, .mkv) is the file that wraps everything together; the codec (H.264, VP9) is how the video inside is compressed. The extension names the container, not the codec, so different extensions can hold the same codec.
03Will converting reduce my video quality?
Only if the codec changes. Rewrapping the same codec into a new container (MOV to MP4 with H.264) is lossless. Re-encoding to a different codec (MP4 to WebM) is generation-lossy, though usually not visibly so at a sensible bitrate.
04Why is conversion slower than on my computer?
The engine is ffmpeg compiled to WebAssembly and runs single-threaded in the tab, without the multi-core and GPU acceleration a native desktop app uses. A re-mux is instant; a full re-encode takes real time. Short clips are best.
05Is there a file size limit?
No hard limit, but the whole file is processed in browser memory, so multi-gigabyte inputs can run the tab out of RAM. For large or long videos, compress or trim first, then convert.
06Do I need to install anything or sign up?
No. It runs in the browser with no install, no account and no watermark. The only download is the ~10 MB engine, fetched once on first use and cached for later.
07Are my files uploaded anywhere?
No. All decoding and encoding happen locally on your device. You can confirm there is no upload in the Network tab of your browser developer tools.
Guides
Further reading
- Guide4 min readBest video format for WhatsApp, Instagram and YouTubeEvery social platform quietly re-encodes what you upload, so the smart move is to hand it a clean file in the shape it wants. One format covers almost all of them — the shape is what changes.Read the guide
- Guide5 min readMP4 vs WebM vs MOV: which format should you use?MP4, WebM and MOV are all video files, but they are not the same kind of thing as the codec inside them. Once you separate the box from what is in it, choosing the right format becomes obvious.Read the guide
- Guide4 min readHow to convert MOV to MP4 (iPhone videos on Windows)You sent an iPhone video to someone on Windows and it would not open. The culprit is Apple's MOV container and the HEVC codec inside it. Here is why, and the one-step fix.Read the guide
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