Make 'build against installed ffmpeg' the default build strategy

.github/workflows/unit_test.yaml

@@ -45,7 +45,7 @@ jobs:
           fi
           # TODO: should we pass -DCMAKE_BUILD_TYPE=Debug here? That's what we
           # do for the C++ tests.
-          python -m pip install -e ".[dev]" --no-build-isolation -vvv
+          BUILD_AGAINST_ALL_FFMPEG_FROM_S3=1 python -m pip install -e ".[dev]" --no-build-isolation -vvv
 
           # list the built so files, for debugging.
           find src | grep ".so"
@@ -87,9 +87,9 @@ jobs:
           ffmpeg -version
       - name: Build and run C++ tests
         run: |
-          export BUILD_AGAINST_INSTALLED_FFMPEG=1
+          unset BUILD_AGAINST_ALL_FFMPEG_FROM_S3
 
-          # Why we need BUILD_AGAINST_INSTALLED_FFMPEG and pkg-config:
+          # Why we're not setting BUILD_AGAINST_ALL_FFMPEG_FROM_S3 here:
           # The C++ tests decode x264 files which is not supported by our
           # pre-built non-GPL FFmpeg libraries. Unfortunately, that's what our
           # C++ tests currently link against by default, which would lead to

setup.py

@@ -89,13 +89,14 @@ def get_ext_filename(self, fullname):
         return ext_filename
 
 
-# If BUILD_AGAINST_INSTALLED_FFMPEG is set, we only build against the installed
-# FFmpeg. We don't know what FFmpeg version that is, so we build
-# `libtorchcodec.so` without any version suffix.
-# If BUILD_AGAINST_INSTALLED_FFMPEG is not set then we want to build against all
+# If BUILD_AGAINST_ALL_FFMPEG_FROM_S3 is set then we want to build against all
 # ffmpeg major version that are available on our S3 bucket.
+# If BUILD_AGAINST_ALL_FFMPEG_FROM_S3 is not set, we only build against the
+# installed FFmpeg. We don't know what FFmpeg version that is, so we build
+# `libtorchcodec.so` without any version suffix. We could probably figure out
+# the version number by invoking `pkg-config --modversion`.
 FFMPEG_MAJOR_VERSIONS = (
-    ("",) if os.getenv("BUILD_AGAINST_INSTALLED_FFMPEG") is not None else (4, 5, 6, 7)
+    (4, 5, 6, 7) if os.getenv("BUILD_AGAINST_ALL_FFMPEG_FROM_S3") is not None else ("",)
 )
 extensions = [
     Extension(

src/torchcodec/decoders/_core/CMakeLists.txt

@@ -49,7 +49,26 @@ function(make_torchcodec_library library_name ffmpeg_target)
     )
 endfunction()
 
-if(DEFINED ENV{BUILD_AGAINST_INSTALLED_FFMPEG})
+if(DEFINED ENV{BUILD_AGAINST_ALL_FFMPEG_FROM_S3})
+    message(
+        STATUS
+        "Building and dynamically linking libtorchcodec against our pre-built
+        non-GPL FFmpeg libraries. These libraries are only used at build time,
+        you still need a different FFmpeg to be installed for run time!"
+    )
+
+    # This will expose the ffmpeg4, ffmpeg5, ffmpeg6, and ffmpeg7 targets
+    include(
+        ${CMAKE_CURRENT_SOURCE_DIR}/fetch_and_expose_non_gpl_ffmpeg_libs.cmake
+    )
+
+    # The libtorchcodec names here must be kept in sync with the library names
+    # in setup.py. Grep for [ LIBTORCHCODEC_KEEP_IN_SYNC ]
+    make_torchcodec_library(libtorchcodec4 ffmpeg4)
+    make_torchcodec_library(libtorchcodec5 ffmpeg5)
+    make_torchcodec_library(libtorchcodec6 ffmpeg6)
+    make_torchcodec_library(libtorchcodec7 ffmpeg7)
+else()
     message(
         STATUS
         "Building and dynamically linking libtorchcodec against the installed
@@ -71,23 +90,4 @@ if(DEFINED ENV{BUILD_AGAINST_INSTALLED_FFMPEG})
     # consistency with the other targets. This can slightly simplify the Python
     # loading and building code as well.
     make_torchcodec_library(libtorchcodec PkgConfig::LIBAV)
-else()
-    message(
-        STATUS
-        "Building and dynamically linking libtorchcodec against our pre-built
-        non-GPL FFmpeg libraries. These libraries are only used at build time,
-        you still a different need FFmpeg to be installed for run time!"
-    )
-
-    # This will expose the ffmpeg4, ffmpeg5, ffmpeg6, and ffmpeg7 targets
-    include(
-        ${CMAKE_CURRENT_SOURCE_DIR}/fetch_and_expose_non_gpl_ffmpeg_libs.cmake
-    )
-
-    # The libtorchcodec names here must be kept in sync with the library names
-    # in setup.py. Grep for [ LIBTORCHCODEC_KEEP_IN_SYNC ]
-    make_torchcodec_library(libtorchcodec4 ffmpeg4)
-    make_torchcodec_library(libtorchcodec5 ffmpeg5)
-    make_torchcodec_library(libtorchcodec6 ffmpeg6)
-    make_torchcodec_library(libtorchcodec7 ffmpeg7)
 endif()

src/torchcodec/decoders/_core/video_decoder_ops.py

@@ -17,7 +17,7 @@ def load_torchcodec_extension():
     # On fbcode, _get_extension_path() is overridden and directly points to the
     # correct .so file, so this for-loop succeeds on the first iteration.
 
-    # grep for BUILD_AGAINST_INSTALLED_FFMPEG to explain the `""` part.
+    # grep for BUILD_AGAINST_ALL_FFMPEG_FROM_S3 to explain the `""` part.
     exceptions = []
     for ffmpeg_major_version in (7, 6, 5, 4, ""):
         library_name = f"libtorchcodec{ffmpeg_major_version}"