Rendley SDK

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FFmpeg ​

The SDK bundles an FFmpeg WASM build for probing, transcoding, and audio mixing during export. Most users never touch it directly, the Engine calls it behind the scenes. Advanced workflows (custom transcoding, direct file operations, building a ZipArchive) can access it through Engine.getInstance().getFFmpeg().

Accessing FFmpeg ​

typescript
const ffmpegModule = Engine.getInstance().getFFmpeg();

Custom WASM Paths ​

If you self-host the FFmpeg WASM bundle (for example, to avoid CDN cold starts), pass your URLs when initializing the Engine:

typescript
await Engine.getInstance().init({
    ffmpeg: {
      coreURL: "https://cdn.yourdomain.com/ffmpeg/ffmpeg-core.js",
      wasmURL: "https://cdn.yourdomain.com/ffmpeg/ffmpeg-core.wasm",
    },
    ...
  });

Retrieve the currently loaded URLs with ffmpegModule.getCoreURL() and ffmpegModule.getWasmURL().

Virtual Filesystem ​

FFmpeg runs in a sandbox with its own in-memory filesystem. Your browser cannot pass native File objects directly; you write bytes in, run commands, and read bytes out.

typescript
// Write a file into the sandbox
await ffmpeg.writeFile(
  "/tmp/input.mp4",
  new Uint8Array(await file.arrayBuffer()),
);

// Check existence
const exists = await ffmpeg.fileExists("/tmp/input.mp4");
const dirExists = await ffmpeg.dirExists("/tmp");

// Read back
const bytes = await ffmpeg.readFile("/tmp/output.mp4");

// Rename and delete
await ffmpeg.rename("/tmp/input.mp4", "/tmp/source.mp4");

Running a Command ​

exec(args[]) runs an FFmpeg command with the usual CLI argument list:

typescript
await ffmpeg.exec([
  "-i",
  "/tmp/input.mp4",
  "-t",
  "5",
  "-c:v",
  "copy",
  "/tmp/first-5-seconds.mp4",
]);

const result = await ffmpeg.readFile("/tmp/first-5-seconds.mp4");

When to Use This Directly ​

Most SDK features handle FFmpeg internally. Reach for direct FFmpeg access when you:

  • Need a file operation the SDK doesn't expose
  • Want to run a one-off transcode or demux outside the Engine's render pipeline.
  • Are building a ZipArchive and need to move files in and out of the sandbox.

See Also ​