Windows: Add FFmpeg build job

.github/workflows/build_ffmpeg.yaml

@@ -70,3 +70,25 @@ jobs:
         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"
+
+  LGPL-Windows:
+    strategy:
+      fail-fast: false
+      matrix:
+        ffmpeg-version: ["4.4.4", "5.1.4", "6.1.1", "7.0.1"]
+    uses: pytorch/test-infra/.github/workflows/windows_job.yml@main
+    with:
+      job-name: Build
+      upload-artifact: ffmpeg-lgpl-windows_x86_64-${{ matrix.ffmpeg-version }}
+      repository: pytorch/torchcodec
+      script: |
+        export FFMPEG_VERSION="${{ matrix.ffmpeg-version }}"
+        export FFMPEG_ROOT="${PWD}/ffmpeg"
+
+        packaging/build_ffmpeg.bat
+
+        tar -cf ffmpeg.tar.gz ffmpeg/include ffmpeg/bin
+
+        artifact_dir="${RUNNER_ARTIFACT_DIR}/$(date +%Y-%m-%d)/windows_$(uname -m)"
+        mkdir -p "${artifact_dir}"
+        mv ffmpeg.tar.gz "${artifact_dir}/${FFMPEG_VERSION}.tar.gz"

packaging/build_ffmpeg.bat

@@ -0,0 +1,10 @@
+:: Taken from torchaudio
+@echo off
+
+set PROJ_FOLDER=%cd%
+
+choco install -y --no-progress msys2 --package-parameters "/NoUpdate"
+C:\tools\msys64\usr\bin\env MSYSTEM=MINGW64 /bin/bash -l -c "pacman -S --noconfirm --needed base-devel mingw-w64-x86_64-toolchain diffutils"
+C:\tools\msys64\usr\bin\env MSYSTEM=MINGW64 /bin/bash -l -c "cd ${PROJ_FOLDER} && packaging/vc_env_helper.bat bash packaging/build_ffmpeg.sh"
+
+:end

packaging/vc_env_helper.bat

@@ -0,0 +1,42 @@
+:: Taken from torchaudio
+@echo on
+
+set VC_VERSION_LOWER=17
+set VC_VERSION_UPPER=18
+
+for /f "usebackq tokens=*" %%i in (`"%ProgramFiles(x86)%\Microsoft Visual Studio\Installer\vswhere.exe" -legacy -products * -version [%VC_VERSION_LOWER%^,%VC_VERSION_UPPER%^) -property installationPath`) do (
+    if exist "%%i" if exist "%%i\VC\Auxiliary\Build\vcvarsall.bat" (
+        set "VS15INSTALLDIR=%%i"
+        set "VS15VCVARSALL=%%i\VC\Auxiliary\Build\vcvarsall.bat"
+        goto vswhere
+    )
+)
+
+:vswhere
+if "%VSDEVCMD_ARGS%" == "" (
+    call "%VS15VCVARSALL%" x64 || exit /b 1
+) else (
+    call "%VS15VCVARSALL%" x64 %VSDEVCMD_ARGS% || exit /b 1
+)
+
+@echo on
+
+if "%CU_VERSION%" == "xpu" call "C:\Program Files (x86)\Intel\oneAPI\setvars.bat"
+
+set DISTUTILS_USE_SDK=1
+
+set args=%1
+shift
+:start
+if [%1] == [] goto done
+set args=%args% %1
+shift
+goto start
+
+:done
+if "%args%" == "" (
+    echo Usage: vc_env_helper.bat [command] [args]
+    echo e.g. vc_env_helper.bat cl /c test.cpp
+)
+
+%args% || exit /b 1