diff --git a/youtube_dl/postprocessor/ffmpeg.py b/youtube_dl/postprocessor/ffmpeg.py
index 5f7298345..8e841b255 100644
--- a/youtube_dl/postprocessor/ffmpeg.py
+++ b/youtube_dl/postprocessor/ffmpeg.py
@@ -274,7 +274,10 @@ class FFmpegExtractAudioPP(FFmpegPostProcessor):
             raise PostProcessingError('WARNING: unable to obtain file audio codec with ffprobe')
 
         more_opts = []
-        if self._preferredcodec == 'best' or self._preferredcodec == filecodec or (self._preferredcodec == 'm4a' and filecodec == 'aac'):
+        if (self._preferredcodec == 'best' 
+            or (self._preferredquality is None 
+                and (self._preferredcodec == filecodec
+                    or (self._preferredcodec == 'm4a' and filecodec == 'aac')))):
             if filecodec == 'aac' and self._preferredcodec in ['m4a', 'best']:
                 # Lossless, but in another container
                 acodec = 'copy'
@@ -325,15 +328,22 @@ class FFmpegExtractAudioPP(FFmpegPostProcessor):
         information['filepath'] = new_path
         information['ext'] = extension
 
-        # If we download foo.mp3 and convert it to... foo.mp3, then don't delete foo.mp3, silly.
-        if (new_path == path
-                or (self._nopostoverwrites and os.path.exists(encodeFilename(new_path)))):
+        # Don't overwrite files if the nopostoverwrites option is active or if
+        # ffmpeg would just copy them anyway
+        if ((new_path == path and acodec == 'copy')
+            or (self._nopostoverwrites and os.path.exists(encodeFilename(new_path)))):
             self._downloader.to_screen('[ffmpeg] Post-process file %s exists, skipping' % new_path)
             return [], information
 
         try:
             self._downloader.to_screen('[ffmpeg] Destination: ' + new_path)
-            self.run_ffmpeg(path, new_path, acodec, more_opts)
+            if new_path == path:
+                temp_filename = prepend_extension(path, 'temp')
+                self.run_ffmpeg(path, temp_filename, acodec, more_opts)
+                os.remove(encodeFilename(path))
+                os.rename(encodeFilename(temp_filename), encodeFilename(path))
+            else:
+                self.run_ffmpeg(path, new_path, acodec, more_opts)
         except AudioConversionError as e:
             raise PostProcessingError(
                 'audio conversion failed: ' + e.msg)
@@ -346,7 +356,10 @@ class FFmpegExtractAudioPP(FFmpegPostProcessor):
                 new_path, time.time(), information['filetime'],
                 errnote='Cannot update utime of audio file')
 
-        return [path], information
+        if new_path == path:
+            return [], information
+        else:
+            return [path], information
 
 
 class FFmpegVideoConvertorPP(FFmpegPostProcessor):