diff --git a/README.md b/README.md
index 01f975958..6766a791d 100644
--- a/README.md
+++ b/README.md
@@ -386,8 +386,12 @@ Alternatively, refer to the [developer instructions](#developer-instructions) fo
 
 ## Post-processing Options:
     -x, --extract-audio              Convert video files to audio-only files
+                                     or convert audio to different format
                                      (requires ffmpeg or avconv and ffprobe or
-                                     avprobe)
+                                     avprobe). Conversion only happens when
+                                     source and target formats are different,
+                                     regardless of source and target quality/
+                                     bitrate
     --audio-format FORMAT            Specify audio format: "best", "aac",
                                      "flac", "mp3", "m4a", "opus", "vorbis", or
                                      "wav"; "best" by default; No effect without