GNOME provides a Videos directory in $HOME folders, place default "Save Folder" location there.
https://launchpad.net/bugs/209592

Index: oggconvert-0.3.3/OggConvert/ocv_main.py
===================================================================
--- oggconvert-0.3.3.orig/OggConvert/ocv_main.py	2010-05-24 20:11.35.536963832 +0100
+++ oggconvert-0.3.3/OggConvert/ocv_main.py	2010-05-24 20:11.35.536963832 +0100
@@ -308,7 +308,11 @@
         self._file_chooser_button.add_filter(audio)
         self._file_chooser_button.add_filter(allfiles)
         
-        self._file_chooser_button.set_current_folder(
+        if os.path.exists(os.path.expanduser("~/Videos")):
+            self._file_chooser_button.set_current_folder(
+                        os.path.expanduser("~/Videos"))
+        else:
+            self._file_chooser_button.set_current_folder(
                         os.path.expanduser("~"))
         
         self._file_chooser_button.set_local_only(False)
