[fbsync] Enable building torchvision with ffmpeg regardless of version on Linux (#4413)

Summary:
* Enable building torchvision with ffmpeg regardless of version on Linux

* Skip tests with python 3.9

* Removed PY39_SKIP

* Cleaned up a bit

Reviewed By: datumbox

Differential Revision: D31268050

fbshipit-source-id: b73ea0ab52e16b26a1e7b960833b5e345d545d3d

Author: NicolasHug

setup.py

@@ -360,14 +360,9 @@ def get_extensions():
         has_ffmpeg = False
     if has_ffmpeg:
         try:
-            # this splits on both dots and spaces as the output format differs across versions / platforms
-            ffmpeg_version_str = str(subprocess.check_output(["ffmpeg", "-version"]))
-            ffmpeg_version = re.split(r"ffmpeg version |\.| |-", ffmpeg_version_str)[1:3]
-            ffmpeg_version = ".".join(ffmpeg_version)
-            if StrictVersion(ffmpeg_version) >= StrictVersion('4.3'):
-                print(f'ffmpeg {ffmpeg_version} not supported yet, please use ffmpeg 4.2.')
-                has_ffmpeg = False
-        except (subprocess.CalledProcessError, IndexError, ValueError):
+            # This is to check if ffmpeg is installed properly.
+            subprocess.check_output(["ffmpeg", "-version"])
+        except subprocess.CalledProcessError:
             print('Error fetching ffmpeg version, ignoring ffmpeg.')
             has_ffmpeg = False