-                                     audio formats, such as  -f
-                                     136/137/mp4/bestvideo,140/m4a/bestaudio
+                                     audio formats, such as -f
+                                     136/137/mp4/bestvideo,140/m4a/bestaudio.
+                                     You can merge the video and audio of two
+                                     formats into a single file using -f <video-
+                                     format>+<audio-format> (requires ffmpeg or
+                                     avconv), for example -f
+                                     bestvideo+bestaudio.