[ffmpeg] Correctly encode paths on Windows

On Python 2.x on Windows, if there are any unicode arguments in the command argument list, the whole list is converted to unicode internally.
Therefore, we need to call encodeArgument on every argument.

Fixes #4337 and #4668.

youtube_dl/postprocessor/ffmpeg.py

@@ -80,8 +80,9 @@ def run_ffmpeg_multiple_files(self, input_paths, out_path, opts):
 
         files_cmd = []
         for path in input_paths:
-            files_cmd.extend(['-i', encodeFilename(path, True)])
-        cmd = ([self._executable, '-y'] + files_cmd
+            files_cmd.extend([encodeArgument('-i'), encodeFilename(path, True)])
+        cmd = ([encodeFilename(self._executable, True), encodeArgument('-y')] +
+               files_cmd
                + [encodeArgument(o) for o in opts] +
                [encodeFilename(self._ffmpeg_filename_argument(out_path), True)])
 
@@ -122,8 +123,8 @@ def get_audio_codec(self, path):
             raise PostProcessingError('ffprobe or avprobe not found. Please install one.')
         try:
             cmd = [
-                self._probe_executable,
-                '-show_streams',
+                encodeFilename(self._probe_executable, True),
+                encodeArgument('-show_streams'),
                 encodeFilename(self._ffmpeg_filename_argument(path), True)]
             handle = subprocess.Popen(cmd, stderr=compat_subprocess_get_DEVNULL(), stdout=subprocess.PIPE)
             output = handle.communicate()[0]