Mention that ffmpeg-harvid is used for mp3 support

include/export-format-profiles.html

@@ -69,6 +69,11 @@
   This column contains a list of Ardour's supported export file types. Selecting
   one updates the options underneath it.
 </p>
+<p>
+	Note: For mp3 export ardour relies on ffmpeg to encode the file. This comes bundled
+	with the video-tools (and is always available when you install the official Ardour
+	binary.
+</p>
 
 <h4>Sample rate</h4>
 <p>

include/video-timeline-setup.html

@@ -22,7 +22,8 @@
     <a href="http://x42.github.io/harvid/" title="http://x42.github.io/harvid/"
     rel="nofollow">http://x42.github.com/harvid/</a></li>
   <li>ffmpeg, ffprobe (used to import/export video, extract soundtracks and query
-    video information): <a href="http://ffmpeg.org" title="http://ffmpeg.org"
+    video information and encode mp3 for export): <a
+    href="http://ffmpeg.org" title="http://ffmpeg.org"
     rel="nofollow">http://ffmpeg.org</a></li>
 </ul>