Fix CI Windows builds (#656)

* Fix FFmpeg version to 5.0.1 for now

* Get FFmpeg from GitHub (no cache sadly)

* Upgrade to ffmpeg 5.1 binaries

.github/workflows/windows-build.yml

@@ -25,24 +25,11 @@ jobs:
           version: 2.15.05
           from-source: false
 
-      - name: FFmpeg hashsum
-        run: |
-          $hashSum = (Invoke-WebRequest 'https://www.gyan.dev/ffmpeg/builds/ffmpeg-release-full-shared.7z.sha256').Content
-          echo "ff_hash=$hashSum" | Out-File $env:GITHUB_ENV -Append
-          Write-Output "Latest release: $hashSum"
-
-      - name: FFmpeg cache
-        id: cache-ff
-        uses: actions/cache@v3
-        with:
-          path: C:/ffmpeg
-          key: ff-${{ env.ff_hash }}
-
       - if: steps.cache-ff.outputs.cache-hit != 'true'
         name: FFmpeg installation
         run: |
           $tempFile = New-TemporaryFile
-          Invoke-WebRequest 'https://www.gyan.dev/ffmpeg/builds/ffmpeg-release-full-shared.7z' -OutFile $tempFile -TimeoutSec 10
+          Invoke-WebRequest 'https://github.com/GyanD/codexffmpeg/releases/download/5.1/ffmpeg-5.1-full_build-shared.7z' -OutFile $tempFile -TimeoutSec 10
           7z x -y -o'C:/ffmpeg' "$tempFile"
 
       - name: FFmpeg environment variable