Build ffmpeg-features in Linux/macOS unittests (#2114)

Summary:
Preparation to land Python front-end of ffmpeg-related features.

- Set BUILD_FFMPEG=1 in Linux/macOS unit test jobs
- Install ffmpeg and pkg-config from conda-forge
- Add note about Windows build process
- Temporarily avoid `av_err2str`

Pull Request resolved: https://github.com/pytorch/audio/pull/2114

Reviewed By: hwangjeff

Differential Revision: D33371346

Pulled By: mthrok

fbshipit-source-id: b0e16a35959a49a2166109068f3e0cbbb836e888

.circleci/unittest/linux/scripts/install.sh

@@ -52,7 +52,7 @@ printf "Installing PyTorch with %s\n" "${cudatoolkit}"
 
 # 2. Install torchaudio
 printf "* Installing torchaudio\n"
-python setup.py install
+BUILD_FFMPEG=1 python setup.py install
 
 # 3. Install Test tools
 printf "* Installing test tools\n"

.circleci/unittest/linux/scripts/setup_env.sh

@@ -40,3 +40,4 @@ conda activate "${env_dir}"
 
 # 3. Install minimal build tools
 pip --quiet install cmake ninja
+conda install --quiet -y -c conda-forge 'ffmpeg>4.1' pkg-config

third_party/CMakeLists.txt

@@ -17,6 +17,16 @@ endif()
 # ffmpeg
 ################################################################################
 if (BUILD_FFMPEG)
+  if(WIN32)
+    message(FATAL_ERROR "FFmpeg integration is not supported on Windows.")
+    # TODO
+    # Since pkg-config is not well-supported on Windows (for example, ffmpeg
+    # installed from conda-forge does not include `.pc` medata file),
+    # to support windows, we need to fill interface manually.
+    #
+    # Something like this might work
+    # https://github.com/microsoft/vcpkg/issues/1379#issuecomment-312483740
+  endif()
   find_package(PkgConfig REQUIRED)
   pkg_check_modules(LIBAV REQUIRED IMPORTED_TARGET
     # requires ffmpeg>=4.1

torchaudio/csrc/ffmpeg/streamer.cpp

@@ -137,7 +137,14 @@ void Streamer::seek(double timestamp) {
   int64_t ts = static_cast<int64_t>(timestamp * AV_TIME_BASE);
   int ret = avformat_seek_file(pFormatContext, -1, INT64_MIN, ts, INT64_MAX, 0);
   if (ret < 0) {
-    throw std::runtime_error(std::string("Failed to seek: ") + av_err2str(ret));
+    // Temporarily removing `av_err2str` function as it causes
+    // `error: taking address of temporary array` on GCC.
+    // TODO:
+    // Workaround with `av_err2string` function from
+    // https://github.com/joncampbell123/composite-video-simulator/issues/5#issuecomment-611885908
+    throw std::runtime_error(std::string("Failed to seek."));
+    // throw std::runtime_error(std::string("Failed to seek: ") +
+    // av_err2str(ret));
   }
 }