FFConvert.py

#FFPMEG Converter GUI
import tkinter,subprocess,os
from tkinter import filedialog,messagebox
from tkinter import *
class FFConvert:
    
    def convert(self):
        
        self.btnConvert['state'] = 'disabled'
        self.btn['state']='disabled'
        if self.file:
            self.txt.delete(0.0,END)
            self.txt.insert(0.0,'File: '+self.filename+'\n')
            ext = self.b.getvar(name='contain') #self.container.get()
            self.txt.insert(END,"Converted Container: "+ext+"\n\n Please Wait...")
            print('contain = '+self.b.getvar(name='contain'))
            cmd=subprocess.run("ffmpeg -i \""+self.file.name+"\" -codec copy -y \""+self.file.name+'.'+ext+"\"",shell=True)
            self.txt.insert(END,cmd)
            if cmd.returncode==0:
                messagebox.showinfo("Done!","Complete")
                self.txt.delete(0.0,END)
                self.txt.insert(END,'DONE!')
                self.btnConvert['state']='normal'
                self.btn['state']='normal'
            else:
                messagebox.showerror("ERROR!","Oops, Error X(")
                self.btn['state']='normal'
                self.btnConvert['state']='normal'
            print(cmd.stdout)
            print('RESULT: '+str(cmd.returncode))
            
    def fileopen(self):
        
        self.file =  filedialog.askopenfile(filetypes=[('all files', '.*'),('AVI', '.avi'),('MP4','.mp4'),('M4P','.m4p'),('MKV','.mkv'),('WMV','.wmv')])
        if self.file:
            self.filename = self.file.name
            print('File: '+self.filename)
            self.btnConvert['state']='normal'

    def __init__(self):
        
        self.gui = Tk()
        self.gui.geometry(newGeometry="300x200")
        self.gui.resizable(width=True, height=True)
        self.gui.title("FFMPEG Converter")
        self.file = None
        self.btn=Button(self.gui,text='Open...',command=self.fileopen)
        self.btn.pack(anchor=E)
        self.container = StringVar()
        self.container.initialize('avi')
        self.container.set('avi')
        self.containers = [("AVI", 'avi'),
                      ("MP4", 'mp4'),
                      ("MKV", 'mkv'),
                      ("WMV", 'wmv'),
                      ("MP3",'mp3'),]  
        for cont, mode in self.containers:
            self.b=Radiobutton(self.gui,indicatoron=1,value=mode,variable='contain',text=cont)
            self.b.pack(anchor=W)
        self.btnConvert = Button(self.gui,text='Convert...',command=self.convert,state='disabled')
        self.btnConvert.pack(anchor=E)
        self.txt=Text(self.gui)
        self.txt.pack(anchor=E)
        self.gui.mainloop()
    
myConvert = FFConvert()

Fixed Error Relating To MessageBox