Most video conversion tools work the same way: you upload your file, wait for the server to process it, then download the result. That means your file — a personal recording, a work presentation, anything confidential — travels to a stranger's server.
ToolZip's video format converter runs entirely in your browser using FFmpeg.wasm. Your file never leaves your device.
Why Video Formats Matter
A video file has two layers: a container (MP4, MKV, AVI) and a codec (H.264, H.265, VP9). The container is the wrapper; the codec is how the video is compressed inside. Same MP4, different codec — and it might not play.
Here's a quick breakdown of the most common formats:
MP4
The universal standard. Plays everywhere — phones, TVs, browsers, messaging apps. Best choice for sharing, uploading to YouTube, sending via WhatsApp or email.
MOV
Apple's native format. iPhone and Mac record in MOV by default. High quality, great for editing — but Windows doesn't play it natively without extra codecs.
WebM
Google's open-source format for the web. Smaller file size than MP4 at the same quality. Perfect for embedding video on websites, but poor support in native apps and messaging.
AVI
Microsoft's legacy format from 1992. Still works on Windows, but massive file sizes and no streaming support make it increasingly irrelevant. No smartphone support.
MKV
The feature-rich container. Supports multiple audio tracks, multiple subtitle tracks, chapters, and almost every codec. Widely used for HD movies — but won't upload to YouTube or send via messaging apps.
When to Convert
| Situation | Target format |
|---|---|
| Upload to YouTube / Instagram | MP4 |
| Send via WhatsApp / KakaoTalk | MP4 |
| iPhone MOV → play on Windows | MP4 |
| MKV movie → smartphone | MP4 |
| Embed video on a website | WebM or MP4 |
| Video editing source file | MOV or MKV |
How the Browser Conversion Works
ToolZip uses FFmpeg compiled to WebAssembly. The entire processing pipeline runs inside your browser tab — no data is transmitted to any server.
Select file
→ FFmpeg.wasm loads (~30MB, cached after first use)
→ Conversion runs locally
→ Download converted file
→ No network request for the file
Verify it yourself: open DevTools → Network tab → convert a video. You'll see the FFmpeg core load once, then nothing. The file stays on your machine.
Implementation
FFmpeg loads from unpkg CDN on first use:
const baseURL = "https://unpkg.com/@ffmpeg/core@0.12.6/dist/umd";
await ffmpeg.load({
coreURL: await toBlobURL(`${baseURL}/ffmpeg-core.js`, "text/javascript"),
wasmURL: await toBlobURL(`${baseURL}/ffmpeg-core.wasm`, "application/wasm"),
});
The conversion command remuxes the container while re-encoding with libx264:
await ffmpeg.exec([
"-i", `input.${inputExt}`,
"-vcodec", "libx264",
"-acodec", "aac",
`output.${targetExt}`
]);
For WebM output, VP9 is used instead:
await ffmpeg.exec([
"-i", `input.${inputExt}`,
"-vcodec", "libvpx-vp9",
"-acodec", "libopus",
"output.webm"
]);
After processing, the result is read back as a Blob and served as a download — no round trip anywhere.
First Load
FFmpeg.wasm is ~30MB. On first use, it loads in 5–15 seconds depending on connection speed. After that, it's cached in the browser and starts instantly on future visits.
This is the cost of running entirely client-side. For privacy-sensitive files, it's worth it.
Supported Conversions
Any combination of: MP4 ↔ MOV ↔ WebM ↔ AVI ↔ MKV
Other Video Tools in ToolZip
All powered by FFmpeg.wasm, all client-side:
| Tool | Description |
|---|---|
| Video Compress | Re-encode with CRF control (High/Medium/Low) |
| Video Trim | Dual-handle range slider with preview before cutting |
| Video to GIF | Clip to GIF with FPS + width control, side-by-side preview |
| Thumbnail Extract | Seek to any frame, save as JPG via Canvas API |
| Audio Extract | Pull MP3 from any video with built-in player |
Try It
toolzip.app/tools/video-convert
No signup. No watermark. No upload. Works on Chrome, Edge, Firefox, and Safari (desktop recommended for large files).
ToolZip — 48 free browser-based tools. Everything runs client-side. toolzip.app