chore(get): factor out ffmpeg download logic (#1021)

### Description of Changes

- Factor out FFmpeg download logic

Author: ayushmanchhabra

README.md

@@ -294,7 +294,6 @@ nwbuild({
 - chore(cli): migrate from `yargs` to `commander`
 - chore(get): verify sha checksum for downloads
 - chore(util): factor out file paths as constant variables
-- chore(get): factor out ffmpeg downloader
 - chore(get): factor out node headers downloader
 - chore(bld): factor out core build step
 - chore(bld): factor out linux config

src/get/ffmpeg.js

@@ -0,0 +1,38 @@
+import path from "node:path";
+
+import request from "./request.js";
+
+/**
+ * Download community FFmpeg binary from `https://github.com/nwjs-ffmpeg-prebuilt/nwjs-ffmpeg-prebuilt`.
+ *
+ * @param  {string}          downloadUrl  - Download server
+ * @param  {string}          version      - Runtime version
+ * @param  {string}          platform     - NW supported platform
+ * @param  {string}          arch         - NW supported architecture
+ * @param  {string}          cacheDir     - Directory to store FFmpeg binary
+ * @return {Promise<string>}              Path of compressed file which containscommunity FFmpeg binary.
+ */
+export default async function ffmpeg(downloadUrl, version, platform, arch, cacheDir) {
+
+  /**
+   * URL to download specific FFmpeg binary from.
+   *
+   * @type {string}
+   */
+  const url = [
+    downloadUrl,
+    version,
+    `${version}-${platform}-${arch}.zip`,
+  ].join('/');
+
+  /**
+   * Absolute path of compressed file which contains FFmpeg binary.
+   */
+  const ffmpegFileAbs = path.resolve(
+    cacheDir,
+    `ffmpeg-${version}-${platform}-${arch}.zip`,
+  );
+  await request(url, ffmpegFileAbs);
+
+  return ffmpegFileAbs;
+}

src/get/ffmpeg.test.js

@@ -0,0 +1,28 @@
+import fs from "node:fs";
+import process from "node:process";
+
+import { afterEach, describe, expect, it } from "vitest";
+
+import util from "../util.js";
+
+import ffmpeg from "./ffmpeg.js";
+
+describe("get/ffmpeg", function () {
+
+  let ffmpegFile = '';
+
+  afterEach(function () {
+    fs.promises.rm(ffmpegFile, { recursive: true, force: true });
+  });
+
+  it("downloades community prebuild FFmpeg for specifc platform", async function () {
+    ffmpegFile = await ffmpeg(
+      "https://github.com/nwjs-ffmpeg-prebuilt/nwjs-ffmpeg-prebuilt/releases/download",
+      "0.83.0",
+      util.PLATFORM_KV[process.platform],
+      util.ARCH_KV[process.arch],
+      "./test/fixture"
+    );
+    expect(util.fileExists(ffmpegFile)).resolves.toBe(true);
+  }, Infinity);
+});