Update usage

apps/website/docs/getting-started/usage.md

@@ -3,30 +3,111 @@
 Learn the basics of using ffmpeg.wasm.
 
 :::note
-It is recommended to read [overview](/docs/overview) to fully understand the
-rationale.
+It is recommended to read [overview](/docs/overview) first.
 :::
 
-## Basic
+## Transcoding AVI video to MP4 video
 
-Converting an AVI video to a MP4 video:
+:::tip
+`Load ffmpeg-core` might take a few minutes to complete as it downloads
+a ~31 MB ffmpeg-core.wasm.
+:::
 
-```js
-import { FFmpeg } from "@ffmpeg/ffmpeg";
-import { fetchFile } from "@ffmpeg/util";
+```jsx live
+function() {
+    const [loaded, setLoaded] = useState(false);
+    const ffmpegRef = useRef(new FFmpeg());
+    const videoRef = useRef(null);
+    const messageRef = useRef(null);
 
-const videoURL = "https://github.com/ffmpegwasm/testdata/raw/master/video-15s.avi";
+    const load = async () => {
+        const ffmpeg = ffmpegRef.current;
+        ffmpeg.on("log", ({ message }) => {
+            messageRef.current.innerHTML = message;
+        });
+        await ffmpeg.load();
+        setLoaded(true);
+    }
 
-(async () => {
-    const ffmpeg = new FFmpeg();
-    // Create a web worker and the worker loads WebAssembly code.
-    await ffmpeg.load();
-    // Write a video file to FS.
-    await ffmpeg.writeFile("input.avi", await fetchFile(videoURL));
-    // Execute ffmpeg command.
-    await ffmpeg.exec(["-i", "input.avi", "output.mp4"]);
-    // Read the output video file from FS, the output file is a Uint8Array typed
-    // array.
-    const data = await ffmpeg.readFile("output.mp4");
-})();
+    const transcode = async () => {
+        const ffmpeg = ffmpegRef.current;
+        await ffmpeg.writeFile(
+            "input.avi",
+            await fetchFile('/video/video-15s.avi')
+        );
+        await ffmpeg.exec(['-i', 'input.avi', 'output.mp4']);
+        const data = await ffmpeg.readFile('output.mp4');
+        videoRef.current.src =
+            URL.createObjectURL(new Blob([data.buffer], {type: 'video/mp4'}));
+    }
+
+    return (loaded
+        ? (
+            <>
+                <video ref={videoRef} controls></video><br/>
+                <button onClick={transcode}>Transcode avi to mp4</button>
+                <p ref={messageRef}></p>
+            </>
+        )
+        : (
+            <button onClick={load}>Load ffmpeg-core</button>
+        )
+    );
+}
+```
+
+## Transcoding AVI video to MP4 video (multi-thread)
+
+:::tip
+`Load ffmpeg-core` might take a few minutes to complete as it downloads
+a ~31 MB ffmpeg-core.wasm.
+:::
+
+```jsx live
+function() {
+    const [loaded, setLoaded] = useState(false);
+    const ffmpegRef = useRef(new FFmpeg());
+    const videoRef = useRef(null);
+    const messageRef = useRef(null);
+
+    const load = async () => {
+        const baseURL = 'https://unpkg.com/@ffmpeg/core-mt@0.12.0-alpha.2/dist/umd'
+        const ffmpeg = ffmpegRef.current;
+        ffmpeg.on("log", ({ message }) => {
+            messageRef.current.innerHTML = message;
+        });
+        await ffmpeg.load({
+            coreURL: await toBlobURL(`${baseURL}/ffmpeg-core.js`),
+            wasmURL: await toBlobURL(`${baseURL}/ffmpeg-core.wasm`),
+            workerURL: await toBlobURL(`${baseURL}/ffmpeg-core.worker.js`),
+            thread: true,
+        });
+        setLoaded(true);
+    }
+
+    const transcode = async () => {
+        const ffmpeg = ffmpegRef.current;
+        await ffmpeg.writeFile(
+            "input.avi",
+            await fetchFile('/video/video-15s.avi')
+        );
+        await ffmpeg.exec(['-i', 'input.avi', 'output.mp4']);
+        const data = await ffmpeg.readFile('output.mp4');
+        videoRef.current.src =
+            URL.createObjectURL(new Blob([data.buffer], {type: 'video/mp4'}));
+    }
+
+    return (loaded
+        ? (
+            <>
+                <video ref={videoRef} controls></video><br/>
+                <button onClick={transcode}>Transcode avi to mp4</button>
+                <p ref={messageRef}></p>
+            </>
+        )
+        : (
+            <button onClick={load}>Load ffmpeg-core</button>
+        )
+    );
+}
 ```