Fix CI FFmpeg setup: scope per-OS + Windows zip extract fallback

The build steps ran download-ffmpeg.js with no arg (default 'both'), so each
runner fetched and extracted *both* platform binaries — coupling each job to
the other OS's extractor. The Windows job then failed because the win .zip is
extracted with unzip, which isn't on the windows-latest runner.

Scope each job to its own platform (linux/win), and make the win extraction
fall back from unzip to bsdtar (tar -xf, present on windows-latest) so the
Windows runner can unpack the zip. Linux/cross-compile dev still use unzip.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: jonberenguer

.github/workflows/build.yml

@@ -22,7 +22,7 @@ jobs:
         run: npm ci
 
       - name: Set up FFmpeg binary
-        run: node scripts/download-ffmpeg.js
+        run: node scripts/download-ffmpeg.js linux
 
       - name: Build Linux AppImage
         run: npm run build:linux
@@ -49,7 +49,7 @@ jobs:
         run: npm ci
 
       - name: Set up FFmpeg binary
-        run: node scripts/download-ffmpeg.js
+        run: node scripts/download-ffmpeg.js win
 
       - name: Build Windows portable
         run: npm run build:win

scripts/download-ffmpeg.js

@@ -59,8 +59,13 @@ const SOURCES = {
     destDir:  path.join(__dirname, '..', 'bin', 'win'),
     destName: 'ffmpeg.exe',
     executable: false,
-    extract: (archivePath, outDir) => execSync(`unzip -o -q "${archivePath}" -d "${outDir}"`, { stdio: 'inherit' }),
-    needs: '`unzip` (apt-get install -y unzip)',
+    // `unzip` on Linux (cross-compile dev / ubuntu CI); fall back to bsdtar's
+    // zip support on the windows-latest runner, which has `tar` but not `unzip`.
+    extract: (archivePath, outDir) => {
+      try { execSync(`unzip -o -q "${archivePath}" -d "${outDir}"`, { stdio: 'inherit' }) }
+      catch { execSync(`tar -xf "${archivePath}" -C "${outDir}"`, { stdio: 'inherit' }) }
+    },
+    needs: '`unzip` (apt-get install -y unzip) or `tar` (bsdtar, default on Windows)',
   },
 }