MP4s definitely seem to not be working right

I'm not entirely sure what's going on with my FFmpeg code, but it's
definitely not generating the proper footers for MP4 files, despite the
fact that the footer function succeeds.  Going to use AVIs for the time
being still.

obs/window-basic-main.cpp

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