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nicolay Armando
nicolay Armando

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Using WebAssembly to Speed Up Video Encoding in the Browser (JS vs WASM Benchmarks)

#webassembly #performance

Browser-based video tools are exploding.

From in-browser editors and recording tools to compression before upload, developers are now expected to handle serious media workloads directly inside the browser. But raw JavaScript hits performance limits quickly.

That’s where WebAssembly (WASM) changes the game.

In this guide, we’ll:

  • Compare native JavaScript vs WASM video encoding
  • Run simple performance benchmarks
  • Use FFmpeg.wasm in a real demo
  • Show practical integration patterns
  • Discuss where this approach actually makes sense in production

If you’re building anything involving video in the browser, this is one of the most valuable performance tools you can learn.

Why WebAssembly Matters for Media Workloads

JavaScript is great — but it was never designed for heavy number crunching like video encoding.

WebAssembly allows you to:

  • Run near-native performance code in the browser
  • Compile C/C++/Rust libraries for web use
  • Handle CPU-intensive workloads without freezing the UI
  • Unlock serious client-side media processing

This shift is especially relevant as more organizations push video creation closer to users: think education platforms, remote teams, public communication tools, and browser-based creative systems. You can see how video ecosystems are evolving across sectors such as education and higher learning and councils and public sector communication, where browser-based tools increasingly matter.

The Experiment: JS Encoder vs WASM Encoder

We’ll compare two approaches:

  1. A simple JavaScript-based processing approach
  2. A WebAssembly-powered encoder using FFmpeg.wasm

Our benchmark goal:

  • Take the same short video
  • Apply a compression/transcode
  • Measure time to completion

We’re not trying to produce a scientific paper — we’re trying to observe practical performance differences.

Baseline: Processing with JavaScript (Canvas-based approach)

A simplified example of JS-heavy processing:

function processFrame(canvas, ctx, video) {
  ctx.drawImage(video, 0, 0, canvas.width, canvas.height);
  const frame = ctx.getImageData(0, 0, canvas.width, canvas.height);

  // Simulate heavy pixel manipulation
  for (let i = 0; i < frame.data.length; i += 4) {
    frame.data[i] = frame.data[i] * 0.9;     // R
    frame.data[i + 1] = frame.data[i + 1];   // G
    frame.data[i + 2] = frame.data[i + 2];   // B
  }

  ctx.putImageData(frame, 0, 0);
}
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This works — but as resolution and frame count increase, performance degrades rapidly. Encoding full videos this way becomes unrealistic.

WASM Approach: FFmpeg.wasm

Now let’s compare that with FFmpeg compiled to WebAssembly.

Install:

npm install @ffmpeg/ffmpeg @ffmpeg/util
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Basic usage:

import { FFmpeg } from '@ffmpeg/ffmpeg';
import { fetchFile } from '@ffmpeg/util';

const ffmpeg = new FFmpeg();

await ffmpeg.load();

await ffmpeg.writeFile('input.mp4', await fetchFile(videoFile));

await ffmpeg.exec([
  '-i', 'input.mp4',
  '-vcodec', 'libx264',
  '-crf', '28',
  'output.mp4'
]);

const data = await ffmpeg.readFile('output.mp4');
const videoBlob = new Blob([data.buffer], { type: 'video/mp4' });
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This is real video encoding happening entirely inside the browser.

No servers. No uploads. Just client-side compute.

Benchmark Results (Typical Observations)

While exact numbers vary by device, typical outcomes look like:

Method 10s 720p video CPU usage UI responsiveness
JS canvas processing Often unusable Very high Freezes frequently
WASM (FFmpeg.wasm) 2–4x faster High but controlled Remains responsive

The takeaway:

WASM doesn't just improve speed — it makes previously impossible workflows actually viable.

This is why we’re seeing more browser-based video tools emerge across creative workflows, internal media systems, and even professional environments documented in real-world project implementations.

Integration Patterns

Integration Patterns That Actually Work

Using WASM successfully isn’t just about raw performance—it’s about architecture.
Patterns that scale:

1. Offload to Web Workers

Never run FFmpeg.wasm on the main thread.

const worker = new Worker('ffmpeg-worker.js');
worker.postMessage({ file });
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2. Progressive UI feedback

Always show:

  • Encoding progress
  • Estimated time
  • Cancel options

FFmpeg.wasm supports progress events.

3. Hybrid architectures

Many real-world systems use:

  • WASM for lightweight client-side compression
  • Server pipelines for heavy transcoding
  • Edge uploads for optimized delivery

This hybrid thinking increasingly mirrors how modern video systems are designed across professional media workflows, something often explored in depth on the creative content and media strategy blog.

When WASM Is the Right Choice (and When It Isn’t)

WASM is excellent for:

  • Client-side compression before upload
  • Browser-based editors
  • Privacy-sensitive video processing
  • Reducing server costs
  • Offline-capable media tools

WASM is not ideal for:

  • Hour-long 4K encodes
  • Large batch processing
  • Battery-sensitive mobile workflows
  • Anything requiring GPU acceleration (yet)

In those cases, server pipelines (like the serverless architectures discussed in earlier posts) still win.

Demo Repo Structure (Suggested)

If you’re sharing this on Dev.to with a GitHub repo, a strong structure looks like:

/wasm-video-demo
  /public
    index.html
  /src
    encoder.js
    worker.js
  /benchmarks
    results.md
  README.md
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In your README, document:

  • Test device
  • Video specs
  • Encoding settings
  • Real timings

That transparency massively increases credibility.

Why This Matters Beyond “Cool Tech”

This isn’t just optimisation for optimisation’s sake.

Client-side media processing unlocks:

  • Faster upload flows
  • Better UX for creators
  • Lower infrastructure costs
  • More private user workflows
  • New kinds of browser-native creative tools

We’re already seeing the ripple effects of this across industries — from education platforms to professional media environments where toolchains increasingly blend browser-based creation with structured production systems such as video media workflows and even dedicated environments like a creative production studio.

dedicated environments

Final Thoughts

WebAssembly doesn’t replace backend pipelines.
It reshapes what’s possible at the edge.

If you’re working with video in the browser and not experimenting with WASM yet, you’re leaving both performance and product opportunities on the table.

The developers who understand this layer well are going to build the next generation of media tools.

If you enjoyed this

You might also enjoy exploring how media workflows, infrastructure, and creative systems intersect across real environments through:

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