How We Built VidStudio with FFmpeg WASM

The Problem with Online Video Tools

Most video editing websites work the same way: you upload your video to their servers, they process it, and you download the result. This creates several problems.

Privacy. Your personal videos sit on someone else's server. Maybe it's a family video, a work recording with confidential information, or something you'd simply rather not share. You're trusting that company to handle your data responsibly.

Speed. Before any processing starts, you have to upload your entire video. On a slow connection, uploading a 500MB file can take 20 minutes. Then you wait for processing. Then you download the result. Most of your time is spent waiting for transfers, not actual editing.

Limits. Free tiers cap file sizes (often 500MB or 1GB). Want to process a longer video? Pay up or look elsewhere.

Dependencies. You need an internet connection, the service needs to stay online, and you're stuck if their servers are slow.

A Different Approach: Processing in Your Browser

VidStudio flips this model. Instead of uploading your video to a server, the processing happens entirely on your own device. Your video file never leaves your browser tab.

This works because of two technologies: FFmpeg and WebAssembly.

What Is FFmpeg?

FFmpeg is a free, open-source project that handles video and audio processing. It's been around since 2000 and powers an enormous amount of the video infrastructure you use daily.

When you watch a YouTube video, FFmpeg encoded it.

When Netflix streams to your TV, FFmpeg processed that stream.

When your phone converts a video, there's a good chance FFmpeg is involved.

FFmpeg can resize, compress, convert, trim, merge, add subtitles, adjust audio, and do essentially anything you'd want with video. Professional video editors use FFmpeg under the hood. It's that capable.

The catch? FFmpeg traditionally runs as a command-line program on your computer. You download it, open a terminal, and type commands. Most people aren't going to do that.

What Is WebAssembly?

WebAssembly (often shortened to WASM) is a way to run programs in web browsers at near-native speed. It lets developers take code written in languages like C or C++ and compile it to run in a browser.

Before WebAssembly, browsers could only run JavaScript. JavaScript is great for websites but wasn't designed for heavy processing like video encoding. WebAssembly fills that gap.

Think of WebAssembly as a translation layer. Programs that normally run on your computer can be compiled to WebAssembly and run in your browser instead. They're not as fast as native applications, but they're close enough for practical use.

FFmpeg + WebAssembly = Browser-Based Video Processing

VidStudio uses ffmpeg.wasm, a version of FFmpeg compiled to run in browsers via WebAssembly. When you open VidStudio and drop in a video, here's what happens:

1. FFmpeg loads in your browser. The first time you visit, your browser downloads the FFmpeg WebAssembly module (about 30MB). It's cached, so subsequent visits are instant.
2. Your video stays local. When you add a video file, it's loaded into your browser's memory. Nothing uploads anywhere.
3. Processing runs on your device. FFmpeg operates on the video using your computer's CPU. Multiple threads handle the work in parallel.
4. Results download directly. The processed video is created in your browser and downloaded to your device. No server involved.

Why This Matters for Privacy

When your video never leaves your device, there's nothing to worry about on the privacy side. No server logs your upload. No database stores your file. No company employee could access it even if they wanted to.

This matters for:

• Personal content. Family videos, home recordings, anything you'd rather keep private.
• Work content. Meeting recordings, internal presentations, confidential material.
• Regulated industries. Healthcare (HIPAA), legal, or any field where data handling has compliance requirements.
• General principle. You shouldn't have to upload personal files to random companies just to resize a video.

Performance: How Fast Is It?

WebAssembly doesn't match native application speed, but it's close enough for practical video editing. A 1-minute 1080p video typically processes in 30 seconds to 2 minutes, depending on your computer and the operation.

Factors that affect speed:

• Your CPU. Faster processors process faster. Multi-core CPUs help since VidStudio uses multiple threads.
• Video resolution. 4K takes longer than 1080p takes longer than 720p.
• Operation type. Simple operations (trimming, audio extraction) are fast. Complex operations (compression with quality targeting) take longer.
• Browser. Chrome and Edge tend to perform best. Firefox and Safari work but may be slightly slower.

The key tradeoff: you skip upload and download time entirely. Even if processing is slightly slower than a server, the total time from start to finish is often faster because you're not waiting for transfers.

Technical Details

For those interested in the specifics:

Library: @ffmpeg/ffmpeg version 0.12.15

Threading: VidStudio uses 1-4 threads depending on the operation. Resize and compression use 2 threads. Audio extraction uses 1. This balances performance with browser stability.

Video codec: H.264 for output (most compatible). The tool accepts most input formats including H.264, H.265, VP9, and older codecs.

Audio codec: AAC for video output. Multiple formats (MP3, WAV, FLAC, AAC) for audio extraction.

Container format: MP4 for video output. This provides the widest compatibility across devices and platforms.

Memory handling: Files are processed in browser memory. Modern browsers handle files up to several gigabytes, though available RAM sets practical limits.

What Can VidStudio Do?

Since VidStudio has the full power of FFmpeg, it handles a wide range of video operations:

• Resize and scale with platform presets, letterboxing, and cropping
• Compress with quality targeting or specific file size goals
• Trim and cut including jump cuts and segment removal
• Extract audio to MP3, WAV, FLAC, or AAC
• Batch process multiple videos to consistent formats
• Add text and subtitles
• Add watermarks (image or text)
• Extract thumbnails and create preview images

Limitations

Browser-based processing has some constraints:

Memory limits. Very large files (many gigabytes) may exceed available browser memory. This depends on your device and how much RAM is free.

Processing speed. WebAssembly is fast, but not as fast as native applications. For quick edits, you won't notice. For processing hours of 4K footage, a desktop application would be faster.

No GPU acceleration. WebAssembly runs on CPU. Hardware video encoding (NVENC, Quick Sync) isn't available. This mostly affects encoding speed for long videos.

Browser compatibility. Modern browsers (Chrome, Firefox, Safari, Edge) all support WebAssembly. Older browsers or unusual configurations might have issues.

For most users doing typical video tasks (resizing for social media, compressing for email, quick trims), these limitations don't matter.

Why We Built It This Way

We wanted a video tool that respects user privacy by default. Not as a premium feature. Not as an afterthought. Just how it works.

Cloud processing is easier to build and scale, but it means handling user files. That comes with responsibility: securing storage, managing data retention, complying with regulations, and earning trust.

Browser-based processing sidesteps all of that. There are no user files on our end because there's no "our end." Your video exists only on your device throughout the entire process.

Frequently Asked Questions

Does VidStudio work offline?

After the initial load, the core functionality works offline. The FFmpeg module caches in your browser. However, you need to be online for the first visit to download the application and FFmpeg library.

Is it really private? How can I verify?

Open your browser's developer tools (Network tab) while using VidStudio. You'll see that video files aren't uploaded anywhere. The only network traffic is loading the application itself.

Why is the first load slower?

The first time you visit, your browser downloads the FFmpeg WebAssembly module (about 30MB). This is cached, so subsequent visits start instantly.

What browsers are supported?

Chrome, Firefox, Safari, and Edge all work. Chrome and Edge tend to have the best performance. Mobile browsers work but process slower than desktop.

Is there a file size limit?

No artificial limits. The practical limit is your device's available memory. Most computers handle videos up to several gigabytes without issue.

Can I use this for work/commercial purposes?

Yes. VidStudio is free to use for any purpose. Since processing happens locally, your work files never touch external servers.