wxPython Convert .ogv (ogg theora) to .avi (GUI)

#!/usr/bin/python
 
# Oggtoavi
# Gentoo dependences
# wxpython
# mplayer with "encode USE set"
 
import os
import sys
import wx
 
class Oggtoavi(wx.Dialog):
    def __init__(self, parent, id, title):
        wx.Dialog.__init__(self, parent, id, title, size=(360, 370))
 
        panel = wx.Panel(self, -1)
        vbox = wx.BoxSizer(wx.VERTICAL)
        hbox1 = wx.BoxSizer(wx.HORIZONTAL)
        hbox2 = wx.BoxSizer(wx.HORIZONTAL)
 
        st1 = wx.StaticText(panel, -1, 'Enter .ogv: ') 
        st2 = wx.StaticText(panel, -1, 'Enter .avi: ')
 
        self.tc1 = wx.TextCtrl(panel, -1, size=(180, -1))
        self.tc2 = wx.TextCtrl(panel, -1, size=(180, -1))
 
        button_send = wx.Button(panel, 1, 'Convert')
 
        hbox1.Add(st1, 0, wx.LEFT, 10)
        hbox1.Add(self.tc1, 0, wx.LEFT, 10)
        hbox2.Add(st2, 0, wx.LEFT, 10)
        hbox2.Add(self.tc2, 0, wx.LEFT, 15)
 
        vbox.Add(hbox1, 0, wx.TOP, 50)
        vbox.Add(hbox2, 0, wx.TOP, 50)
        vbox.Add(button_send, 0, wx.ALIGN_CENTER | wx.TOP | wx.TOP | wx.BOTTOM, 100)
 
        self.Bind(wx.EVT_BUTTON, self.OnConvert, id=1)
        panel.SetSizer(vbox)
 
        self.Centre()
        self.ShowModal()
        self.Destroy()
 
    def OnConvert(self, event):
        ogg = self.tc1.GetValue()
        avi = self.tc2.GetValue()
 
        os.system("mencoder %s -ovc lavc -oac mp3lame -o %s" % (ogg, avi)) 
        if os.path.exists(avi):
            dlg = wx.MessageDialog(self, 'Your .avi file was created.', 'Success', wx.OK | wx.ICON_INFORMATION)
            dlg.ShowModal()
            dlg.Destroy()
            sys.exit()
        else:
            dlg = wx.MessageDialog(self, 'Failed to convert.', 'Error', wx.OK | wx.ICON_ERROR)
 
            dlg.ShowModal()
            dlg.Destroy()
            sys.exit()
 
app = wx.App()
Oggtoavi(None, -1, 'Oggtoavi')
app.MainLoop()