Add Mac to FFmpeg build CI

.github/workflows/build_ffmpeg.yaml

@@ -9,10 +9,15 @@
 # par new major release of FFmepg.
 name: Build non-GPL FFmpeg from source
 
-on:
-  workflow_dispatch:
-  schedule:
-    - cron: '0 0 * * 0'  # on sunday
+#on:
+#  workflow_dispatch:
+#  schedule:
+#    - cron: '0 0 * * 0'  # on sunday
+#
+on: # temp for testing; tell Scott to remove this if under review
+  push:
+    branches: [ main ]
+  pull_request:
 
 defaults:
   run:
@@ -43,3 +48,26 @@ jobs:
         with:
           name: "ffmpeg_${{ matrix.ffmpeg-version }}_linux_x86_64"
           path: artifact_dir
+  LGPL-macOS:
+    strategy:
+      fail-fast: false
+      matrix:
+        ffmpeg_version: ["4.4.4", "5.1.4", "6.1.1", "master"]
+        runner: ["macos-m1-stable", "macos-12"]
+    uses: pytorch/test-infra/.github/workflows/macos_job.yml@main
+    with:
+      job-name: Build
+      upload-artifact: ffmpeg-lgpl
+      repository: pytorch/torchcodec
+      runner: "${{ matrix.runner }}"
+      script: |
+        export FFMPEG_VERSION="${{ matrix.ffmpeg_version }}"
+        export FFMPEG_ROOT="${PWD}/ffmpeg"
+
+        packaging/build_ffmpeg.sh
+
+        tar -czf ffmpeg.tar.gz ffmpeg/include ffmpeg/lib
+
+        artifact_dir="${RUNNER_ARTIFACT_DIR}/$(date +%Y-%m-%d)/macos_$(uname -m)"
+        mkdir -p "${artifact_dir}"
+        mv ffmpeg.tar.gz "${artifact_dir}/${FFMPEG_VERSION}.tar.gz"