How to Stream Data Efficiently in the Browser with WebCodecs API

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The WebCodecs API is a powerful, low-level browser API that provides direct access to media encoding and decoding components. It allows web developers to stream video and audio efficiently, skipping the traditional <video> pipeline and instead integrating with tools like WebTransport, WebRTC, or WebAssembly.

What Is WebCodecs?


WebCodecs enables developers to decode and encode media directly in the browser using JavaScript. It gives you control over performance-critical parts of a media pipeline — a big win for game streaming, real-time communication, and in-browser editing tools.

Why Use WebCodecs?

• Low latency: No need to wait for video elements to decode.
• Hardware acceleration: Uses built-in GPU/CPU codecs.
• Flexible: Works great with WebAssembly and streaming APIs.
• Ideal for custom pipelines: e.g., decode video with WebCodecs and transmit it with WebTransport.

How to Decode a Video Stream Using WebCodecs


Let’s say you receive encoded video data from a WebTransport stream. You can decode it using WebCodecs like this:

const videoDecoder = new VideoDecoder({
output: frame => {
const ctx = canvas.getContext("2d");
ctx.drawImage(frame, 0, 0);
frame.close();
},
error: err => console.error("Decoding error:", err)
});

videoDecoder.configure({
codec: "vp8",
width: 640,
height: 480,
});

webTransportStream.readable.getReader().read().then(({ value }) => {
videoDecoder.decode(new EncodedVideoChunk({
type: "key",
timestamp: 0,
data: value
}));
});

Encoding Video with WebCodecs


You can also encode a video stream to send elsewhere:

const encoder = new VideoEncoder({
output: chunk => {
sendToTransport(chunk);
},
error: err => console.error("Encoding error:", err)
});

encoder.configure({
codec: "vp8",
width: 640,
height: 480,
framerate: 30,
});

const stream = canvas.captureStream();
const track = stream.getVideoTracks()[0];
const processor = new MediaStreamTrackProcessor({ track });

const reader = processor.readable.getReader();
reader.read().then(function process({ value, done }) {
if (done) return;
encoder.encode(value);
value.close();
return reader.read().then(process);
});

Use Cases

• Low-latency video chat with custom pipelines
• In-browser screen or game capture with real-time encoding
• Video editing tools built in WebAssembly
• Streaming to WebTransport or WebRTC with precise control

Browser Support


WebCodecs is currently supported in Chromium-based browsers (Chrome 94+, Edge). Safari and Firefox support is under consideration or partially available behind flags.

Conclusion


WebCodecs opens the door for new categories of high-performance web applications, especially in real-time streaming and multimedia editing. It’s an advanced tool that rewards those building custom pipelines where performance is critical.

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