Install FFmpeg as a requirement

.github/workflows/tests_all.yml

@@ -12,11 +12,19 @@ jobs:
 
     steps:
     - uses: actions/checkout@v3
+
     - name: Set up Python
       uses: actions/setup-python@v4
       with:
         python-version: '3.12'
 
+    - uses: FedericoCarboni/setup-ffmpeg@v3
+      # install ffmpeg as special requirement
+      id: setup-ffmpeg
+      with:
+        ffmpeg-version: release
+        github-token: ${{ github.server_url == 'https://github.com' && github.token || '' }}
+
     - name: Install dependencies
       # install all requirements
       run: |