Add `is_ffmpeg_available` in test (#2170)

Summary:
Part of https://github.com/pytorch/audio/issues/2164.
To make the tests introduced in https://github.com/pytorch/audio/issues/2164 skippable if ffmpeg features are not available,
this commit adds `is_ffmpeg_available`.

The availability of the features depend on two factors;
1. If it was enabled at build.
2. If the ffmpeg libraries are found at runtime.

A simple way (for OSS workflow) to detect these is simply checking if
`libtorchaudio_ffmpeg` presents and can be loaded without a failure.

To facilitate this, this commit changes the
`torchaudio._extension._load_lib` to return boolean result.

Pull Request resolved: https://github.com/pytorch/audio/pull/2170

Reviewed By: carolineechen

Differential Revision: D33797695

Pulled By: mthrok

fbshipit-source-id: 85e767fc06350b8f99de255bc965b8c92b8cfe97

test/torchaudio_unittest/common_utils/__init__.py

@@ -7,6 +7,7 @@ from .case_utils import (
     TestBaseMixin,
     PytorchTestCase,
     TorchaudioTestCase,
+    is_ffmpeg_available,
     skipIfNoCtcDecoder,
     skipIfNoCuda,
     skipIfNoExec,
@@ -15,6 +16,7 @@ from .case_utils import (
     skipIfNoSox,
     skipIfRocm,
     skipIfNoQengine,
+    skipIfNoFFmpeg,
 )
 from .data_utils import (
     get_asset_path,
@@ -31,7 +33,6 @@ from .wav_utils import (
     save_wav,
 )
 
-
 __all__ = [
     "get_asset_path",
     "get_whitenoise",
@@ -43,6 +44,7 @@ __all__ = [
     "TestBaseMixin",
     "PytorchTestCase",
     "TorchaudioTestCase",
+    "is_ffmpeg_available",
     "skipIfNoCtcDecoder",
     "skipIfNoCuda",
     "skipIfNoExec",
@@ -52,6 +54,7 @@ __all__ = [
     "skipIfNoSoxBackend",
     "skipIfRocm",
     "skipIfNoQengine",
+    "skipIfNoFFmpeg",
     "get_wav_data",
     "normalize_wav",
     "load_wav",

test/torchaudio_unittest/common_utils/case_utils.py

@@ -7,6 +7,7 @@ import time
 import unittest
 
 import torch
+import torchaudio
 from torch.testing._internal.common_utils import TestCase as PytorchTestCase
 from torchaudio._internal.module_utils import is_module_available, is_sox_available, is_kaldi_available
 
@@ -95,6 +96,13 @@ class TorchaudioTestCase(TestBaseMixin, PytorchTestCase):
     pass
 
 
+def is_ffmpeg_available():
+    try:
+        return torchaudio._extension._load_lib("libtorchaudio_ffmpeg")
+    except Exception:
+        return False
+
+
 def _eval_env(var, default):
     if var not in os.environ:
         return default
@@ -199,3 +207,8 @@ skipIfNoQengine = _skipIf(
     reason="`fbgemm` is not available.",
     key="NO_QUANTIZATION",
 )
+skipIfNoFFmpeg = _skipIf(
+    not is_ffmpeg_available(),
+    reason="ffmpeg features are not available.",
+    key="NO_FFMPEG",
+)

torchaudio/_extension.py

@@ -14,15 +14,43 @@ def _get_lib_path(lib: str):
     return path
 
 
-def _load_lib(lib: str):
+def _load_lib(lib: str) -> bool:
+    """Load extension module
+
+    Note:
+        In case `torchaudio` is deployed with `pex` format, the library file
+        is not in a standard location.
+        In this case, we expect that `libtorchaudio` is available somewhere
+        in the search path of dynamic loading mechanism, so that importing
+        `_torchaudio` will have library loader find and load `libtorchaudio`.
+        This is the reason why the function should not raising an error when the library
+        file is not found.
+
+    Returns:
+        bool:
+            True if the library file is found AND the library loaded without failure.
+            False if the library file is not found (like in the case where torchaudio
+            is deployed with pex format, thus the shared library file is
+            in a non-standard location.).
+            If the library file is found but there is an issue loading the library,
+            (such as missing dependency) then this function raises the exception as-is.
+
+    Raises:
+        Exception:
+            If the library file is found, but there is an issue loading the library file,
+            (when underlying `ctype.DLL` throws an exception), this function will pass
+            the exception as-is, instead of catching it and returning bool.
+            The expected case is `OSError` thrown by `ctype.DLL` when a dynamic dependency
+            is not found.
+            This behavior was chosen because the expected failure case is not recoverable.
+            If a dependency is missing, then users have to install it.
+    """
     path = _get_lib_path(lib)
-    # In case `torchaudio` is deployed with `pex` format, this file does not exist.
-    # In this case, we expect that `libtorchaudio` is available somewhere
-    # in the search path of dynamic loading mechanism, and importing `_torchaudio`,
-    # which depends on `libtorchaudio` and dynamic loader will handle it for us.
-    if path.exists():
+    if not path.exists():
+        return False
     torch.ops.load_library(path)
     torch.classes.load_library(path)
+    return True
 
 
 def _init_extension():