Don't use 2.7+ check_output

youtube_dl/PostProcessor.py

@@ -73,7 +73,7 @@ class FFmpegExtractAudioPP(PostProcessor):
 	def detect_executables():
 		def executable(exe):
 			try:
-				subprocess.check_output([exe, '-version'])
+				subprocess.Popen([exe, '-version'], stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate()
 			except OSError:
 				return False
 			return exe