Build ffmpeg-features on macOS wheel binary dist (#2122)

Summary:
This commit enable ffmpeg-feature build on wheel-based binary distribution on macOS.

For macOS, since the underlying Python env is Conda, it installs `ffmpeg` from conda.

Depends on https://github.com/pytorch/audio/issues/1873

Pull Request resolved: https://github.com/pytorch/audio/pull/2122

Reviewed By: carolineechen, nateanl

Differential Revision: D33409113

Pulled By: mthrok

fbshipit-source-id: a73839087548010353422109b33e89e262c12a57

.circleci/config.yml

@@ -204,6 +204,8 @@ jobs:
             sh conda.sh -b
             source $HOME/miniconda3/bin/activate
             packaging/build_wheel.sh
+          environment:
+            BUILD_FFMPEG: true
       - store_artifacts:
           path: dist
       - persist_to_workspace:

.circleci/config.yml.in

@@ -204,6 +204,8 @@ jobs:
             sh conda.sh -b
             source $HOME/miniconda3/bin/activate
             packaging/build_wheel.sh
+          environment:
+            BUILD_FFMPEG: true
       - store_artifacts:
           path: dist
       - persist_to_workspace:

packaging/pkg_helpers.bash

@@ -183,7 +183,7 @@ setup_wheel_python() {
     conda create -yn "env$PYTHON_VERSION" python="$PYTHON_VERSION"
     conda activate "env$PYTHON_VERSION"
     if [[ "$(uname)" == Darwin ]]; then
-        conda install --quiet -y pkg-config
+        conda install --quiet -y pkg-config "ffmpeg>=4.1"
     fi
   else
     case "$PYTHON_VERSION" in