必要なライブラリは適宜ダウンロードしてください。
ytdownload_bestaudio.py
# -*- coding: utf-8 -*-

from PIL import ImageGrab, Image
import tkinter
import time as tm1 
import datetime as dt1
import pyperclip 
import os 
from youtube_dl import YoutubeDL

class Application( tkinter.Frame ):
    def __init__(self, master): 
        super().__init__(master) 
        self.flag1 = 0 
        self.path1 = os.path.dirname(__file__) + "\\" 
        self.pack() 
        master.title(u"clipboard capture")
        master.geometry("300x40")
        self.label1 = tkinter.Label(text='')
        self.label1.place(x=10, y=10) 
        self.btn1 = tkinter.Button(master, text='start', command=self.btn_click1, bg='orange')
        self.btn1.place(x=180, y=10, width=100)
        master.after(2000, self.update) 

    def update(self): 
        if self.flag1 == 1: 
            datetime1 = dt1.datetime.now().strftime( "%Y%m%d_%H%M%S" ) 
            file1 = datetime1
            self.label1["text"] = file1 
            ret1 = 0 
            ret1 = self.capture1( file1 ) 
        self.master.after(2000, self.update) 

    def capture1( self, file0 ): 
        ret1 = "0" 
        im1 = ImageGrab.grabclipboard()
        str1 = pyperclip.paste().strip().replace( "\r\n", "\n" )
        pyperclip.copy("")
        if "www.youtube.com" in str1:
            print( str1 ) 
            ytdl( str1 )
            ret1 = "1" 
        elif str1 != "": 
            print( str1 ) 
            file1 = self.path1 + str(file0) + ".txt" 
            write1( file1, str1 ) 
            ret1 = "1" 
        elif isinstance(im1, Image.Image):
            file1 = self.path1 + str(file0) + ".jpg" 
            print( file1 ) 
            im1.save( file1 )
            ret1 = "1" 
        return ret1 

    def btn_click1( self ): 
        self.label1.config( text = '' ) 
        if self.flag1 == 0:
            self.flag1 = 1 
            self.btn1.config(bg = 'red', text = 'stop' ) 
        else: 
            self.flag1 = 0 
            self.btn1.config(bg = 'orange', text = 'start' ) 

def write1( file1, str1 ): 
    with open( file1, 'w', encoding='utf-8' ) as f1: 
        f1.write( str1 ) 
    return 0 

def ytdl( str1 ):
    meta = YoutubeDL().extract_info(str1, download=False)
    title = meta.get('title')
    ext = meta.get('ext')
    ydl_opts = {
        'format': 'bestaudio/best',
        'outtmpl': '%(title)s' + '.%(ext)s'
    }
    with YoutubeDL(ydl_opts) as yt:
        yt.download([str1])
        yt.cache.remove()

def main(): 
    root = tkinter.Tk()
    app = Application( master=root ) 
    app.mainloop()

if __name__ == "__main__": 
    main()