Added a comment about DirectSound codecs.

modules/juce_video/native/juce_win32_DirectShowComponent.cpp

@@ -359,6 +359,9 @@ public:
             return true;
         }
 
+        // Note that if you're trying to open a file and this method fails, you may
+        // just need to install a suitable codec. It seems that by default DirectShow
+        // doesn't support a very good range of formats.
         release();
         return false;
     }