Merge remote-tracking branch 'ivan/muxed-mtime'

diff --cc youtube_dl/postprocessor/ffmpeg.py
index 6e9194fa6ae94f5beeb03d1e6a50ae0853242465,d44de84cf1698623b9be19fe640600609dc1a704..8bf5bebc31bb06ce57a86a2216aea2044dbb0bfc
--- 1/youtube_dl/postprocessor/ffmpeg.py
--- 2/youtube_dl/postprocessor/ffmpeg.py
+++ b/youtube_dl/postprocessor/ffmpeg.py
@@@ -82,12 -76,12 +82,14 @@@ class FFmpegPostProcessor(PostProcessor
      def run_ffmpeg_multiple_files(self, input_paths, out_path, opts):
          self.check_version()
  
++        oldest_mtime = min(os.stat(path).st_mtime for path in input_paths)
++
          files_cmd = []
          for path in input_paths:
 -            files_cmd.extend(['-i', encodeFilename(path, True)])
 -        oldest_mtime = min(os.stat(path).st_mtime for path in input_paths)
 -        cmd = ([self._executable, '-y'] + files_cmd
 -               + [encodeArgument(o) for o in opts] +
 +            files_cmd.extend([encodeArgument('-i'), encodeFilename(path, True)])
 +        cmd = ([encodeFilename(self._executable, True), encodeArgument('-y')] +
-                files_cmd
-                + [encodeArgument(o) for o in opts] +
++               files_cmd +
++               [encodeArgument(o) for o in opts] +
                 [encodeFilename(self._ffmpeg_filename_argument(out_path), True)])
  
          if self._downloader.params.get('verbose', False):