https://stackoverflow.com/questions/49185538/how-to-add-progress-bar

ダウンロードする前にprogress表示用のコールバック関数をセットしておけば良いみたい

```
self.size=0

# new
def progress_func(self,stream, chunk,file_handle, bytes_remaining):
    # size = video.filesize
    # p = 0
    # while p <= 100:
        # progress = p
        # print str(p)+'%'
        # p = percent(bytes_remaining, self.size)
    # print(bytes_remaining , self.size ) 
    print(round((1-bytes_remaining/self.size)*100, 3), '% done...')


# new
def percent(self, tem, total):
    perc = (float(tem) / float(total)) * float(100)
    return perc


# rewrite
def btn_download( self, event ):

    yt = YouTube( self.m_textCtrl1.GetValue(), on_progress_callback=progress_func)
    video=yt.streams.get_by_itag( self.m_textCtrl3.GetValue() )
    self.size=video.filesize
    print(self.size)
    video.download( self.m_textCtrl2.GetValue() )

```