Use MP4s when not on windows

Also, make it use 'veryfast' preset.  Still testing this, might have to
revise this later.

obs/window-basic-main.cpp

@@ -601,7 +601,12 @@ void OBSBasic::on_recordButton_clicked()
 	} else {
 		QString path = QFileDialog::getSaveFileName(this,
 				"Please enter a file name", QString(),
-				"Video Files (*.avi)");
+#ifdef _WIN32
+				"AVI Files (*.avi)"
+#else
+				"MP4 Files (*.mp4)"
+#endif
+				);
 
 		if (path.isNull() || path.isEmpty())
 			return;