OSD sizes in percent; automatic update of OSD size

PLUGINS.html

@@ -1939,6 +1939,17 @@ user - whether this goes through OSD facilities of the physical device (like
 a "full featured" DVB card) or through a graphics adapter that overlays its
 output with the video signal, doesn't matter.
 
+<div class="modified">
+In order to be able to determine the proper size of the OSD, the device
+should implement the function
+
+<p><table><tr><td class="code"><pre>
+virtual void GetVideoSize(int &amp;Width, int &amp;Height, eVideoAspect &amp;Aspect);
+</pre></td></tr></table><p>
+
+By default, an OSD size of 480x324 with an aspect ratio of 4:3 is assumed.
+</div modified>
+
 <p>
 <b>Initializing new devices</b>
 <p>