Make dlopen ffmpeg default off (#3418)

Summary:
To investigate https://github.com/pytorch/audio/issues/3411

Pull Request resolved: https://github.com/pytorch/audio/pull/3418

Differential Revision: D46535891

Pulled By: mthrok

fbshipit-source-id: b90bba399eb54f9f0ae073bd590cd8a46054ed7e

tools/setup_helpers/extension.py

@@ -37,7 +37,7 @@ _BUILD_SOX = False if platform.system() == "Windows" else _get_build("BUILD_SOX"
 _BUILD_RIR = _get_build("BUILD_RIR", True)
 _BUILD_RNNT = _get_build("BUILD_RNNT", True)
 _USE_FFMPEG = _get_build("USE_FFMPEG", False)
-_DLOPEN_FFMPEG = _get_build("DLOPEN_FFMPEG", True)
+_DLOPEN_FFMPEG = _get_build("DLOPEN_FFMPEG", False)
 _USE_ROCM = _get_build("USE_ROCM", torch.backends.cuda.is_built() and torch.version.hip is not None)
 _USE_CUDA = _get_build("USE_CUDA", torch.backends.cuda.is_built() and torch.version.hip is None)
 _BUILD_ALIGN = _get_build("BUILD_ALIGN", True)